bs4源码

Beautiful源码：

"""Beautiful Soup
Elixir and Tonic
"The Screen-Scraper's Friend"
http://www.crummy.com/software/BeautifulSoup/
 
Beautiful Soup uses a pluggable XML or HTML parser to parse a
(possibly invalid) document into a tree representation. Beautiful Soup
provides methods and Pythonic idioms that make it easy to navigate,
search, and modify the parse tree.
 
Beautiful Soup works with Python 2.7 and up. It works better if lxml
and/or html5lib is installed.
 
For more than you ever wanted to know about Beautiful Soup, see the
documentation:
http://www.crummy.com/software/BeautifulSoup/bs4/doc/
 
"""
 
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
 
__author__ = "Leonard Richardson (leonardr@segfault.org)"
__version__ = "4.6.3"
__copyright__ = "Copyright (c) 2004-2018 Leonard Richardson"
__license__ = "MIT"
 
__all__ = ['BeautifulSoup']
 
import os
import re
import sys
import traceback
import warnings
 
from .builder import builder_registry, ParserRejectedMarkup
from .dammit import UnicodeDammit
from .element import (
    CData,
    Comment,
    DEFAULT_OUTPUT_ENCODING,
    Declaration,
    Doctype,
    NavigableString,
    PageElement,
    ProcessingInstruction,
    ResultSet,
    SoupStrainer,
    Tag,
    )
 
# The very first thing we do is give a useful error if someone is
# running this code under Python 3 without converting it.
'You are trying to run the Python 2 version of Beautiful Soup under Python 3. This will not work.'!='You need to convert the code, either by installing it (`python setup.py install`) or by running 2to3 (`2to3 -w bs4`).'
 
class BeautifulSoup(Tag):
    """
    This class defines the basic interface called by the tree builders.
 
    These methods will be called by the parser:
      reset()
      feed(markup)
 
    The tree builder may call these methods from its feed() implementation:
      handle_starttag(name, attrs) # See note about return value
      handle_endtag(name)
      handle_data(data) # Appends to the current data node
      endData(containerClass=NavigableString) # Ends the current data node
 
    No matter how complicated the underlying parser is, you should be
    able to build a tree using 'start tag' events, 'end tag' events,
    'data' events, and "done with data" events.
 
    If you encounter an empty-element tag (aka a self-closing tag,
    like HTML's <br> tag), call handle_starttag and then
    handle_endtag.
    """
    ROOT_TAG_NAME = '[document]'
 
    # If the end-user gives no indication which tree builder they
    # want, look for one with these features.
    DEFAULT_BUILDER_FEATURES = ['html', 'fast']
 
    ASCII_SPACES = '\x20\x0a\x09\x0c\x0d'
 
    NO_PARSER_SPECIFIED_WARNING = "No parser was explicitly specified, so I'm using the best available %(markup_type)s parser for this system (\"%(parser)s\"). This usually isn't a problem, but if you run this code on another system, or in a different virtual environment, it may use a different parser and behave differently.\n\nThe code that caused this warning is on line %(line_number)s of the file %(filename)s. To get rid of this warning, pass the additional argument 'features=\"%(parser)s\"' to the BeautifulSoup constructor.\n"
 
    def __init__(self, markup="", features=None, builder=None,
                 parse_only=None, from_encoding=None, exclude_encodings=None,
                 **kwargs):
        """Constructor.
 
        :param markup: A string or a file-like object representing
        markup to be parsed.
 
        :param features: Desirable features of the parser to be used. This
        may be the name of a specific parser ("lxml", "lxml-xml",
        "html.parser", or "html5lib") or it may be the type of markup
        to be used ("html", "html5", "xml"). It's recommended that you
        name a specific parser, so that Beautiful Soup gives you the
        same results across platforms and virtual environments.
 
        :param builder: A specific TreeBuilder to use instead of looking one
        up based on `features`. You shouldn't need to use this.
 
        :param parse_only: A SoupStrainer. Only parts of the document
        matching the SoupStrainer will be considered. This is useful
        when parsing part of a document that would otherwise be too
        large to fit into memory.
 
        :param from_encoding: A string indicating the encoding of the
        document to be parsed. Pass this in if Beautiful Soup is
        guessing wrongly about the document's encoding.
 
        :param exclude_encodings: A list of strings indicating
        encodings known to be wrong. Pass this in if you don't know
        the document's encoding but you know Beautiful Soup's guess is
        wrong.
 
        :param kwargs: For backwards compatibility purposes, the
        constructor accepts certain keyword arguments used in
        Beautiful Soup 3. None of these arguments do anything in
        Beautiful Soup 4 and there's no need to actually pass keyword
        arguments into the constructor.
        """
 
        if 'convertEntities' in kwargs:
            warnings.warn(
                "BS4 does not respect the convertEntities argument to the "
                "BeautifulSoup constructor. Entities are always converted "
                "to Unicode characters.")
 
        if 'markupMassage' in kwargs:
            del kwargs['markupMassage']
            warnings.warn(
                "BS4 does not respect the markupMassage argument to the "
                "BeautifulSoup constructor. The tree builder is responsible "
                "for any necessary markup massage.")
 
        if 'smartQuotesTo' in kwargs:
            del kwargs['smartQuotesTo']
            warnings.warn(
                "BS4 does not respect the smartQuotesTo argument to the "
                "BeautifulSoup constructor. Smart quotes are always converted "
                "to Unicode characters.")
 
        if 'selfClosingTags' in kwargs:
            del kwargs['selfClosingTags']
            warnings.warn(
                "BS4 does not respect the selfClosingTags argument to the "
                "BeautifulSoup constructor. The tree builder is responsible "
                "for understanding self-closing tags.")
 
        if 'isHTML' in kwargs:
            del kwargs['isHTML']
            warnings.warn(
                "BS4 does not respect the isHTML argument to the "
                "BeautifulSoup constructor. Suggest you use "
                "features='lxml' for HTML and features='lxml-xml' for "
                "XML.")
 
        def deprecated_argument(old_name, new_name):
            if old_name in kwargs:
                warnings.warn(
                    'The "%s" argument to the BeautifulSoup constructor '
                    'has been renamed to "%s."' % (old_name, new_name))
                value = kwargs[old_name]
                del kwargs[old_name]
                return value
            return None
 
        parse_only = parse_only or deprecated_argument(
            "parseOnlyThese", "parse_only")
 
        from_encoding = from_encoding or deprecated_argument(
            "fromEncoding", "from_encoding")
 
        if from_encoding and isinstance(markup, str):
            warnings.warn("You provided Unicode markup but also provided a value for from_encoding. Your from_encoding will be ignored.")
            from_encoding = None
 
        if len(kwargs) > 0:
            arg = list(kwargs.keys()).pop()
            raise TypeError(
                "__init__() got an unexpected keyword argument '%s'" % arg)
 
        if builder is None:
            original_features = features
            if isinstance(features, str):
                features = [features]
            if features is None or len(features) == 0:
                features = self.DEFAULT_BUILDER_FEATURES
            builder_class = builder_registry.lookup(*features)
            if builder_class is None:
                raise FeatureNotFound(
                    "Couldn't find a tree builder with the features you "
                    "requested: %s. Do you need to install a parser library?"
                    % ",".join(features))
            builder = builder_class()
            if not (original_features == builder.NAME or
                    original_features in builder.ALTERNATE_NAMES):
                if builder.is_xml:
                    markup_type = "XML"
                else:
                    markup_type = "HTML"
 
                # This code adapted from warnings.py so that we get the same line
                # of code as our warnings.warn() call gets, even if the answer is wrong
                # (as it may be in a multithreading situation).
                caller = None
                try:
                    caller = sys._getframe(1)
                except ValueError:
                    pass
                if caller:
                    globals = caller.f_globals
                    line_number = caller.f_lineno
                else:
                    globals = sys.__dict__
                    line_number= 1
                filename = globals.get('__file__')
                if filename:
                    fnl = filename.lower()
                    if fnl.endswith((".pyc", ".pyo")):
                        filename = filename[:-1]
                if filename:
                    # If there is no filename at all, the user is most likely in a REPL,
                    # and the warning is not necessary.
                    values = dict(
                        filename=filename,
                        line_number=line_number,
                        parser=builder.NAME,
                        markup_type=markup_type
                    )
                    warnings.warn(self.NO_PARSER_SPECIFIED_WARNING % values, stacklevel=2)
 
        self.builder = builder
        self.is_xml = builder.is_xml
        self.known_xml = self.is_xml
        self.builder.soup = self
 
        self.parse_only = parse_only
 
        if hasattr(markup, 'read'):        # It's a file-type object.
            markup = markup.read()
        elif len(markup) <= 256 and (
                (isinstance(markup, bytes) and not b'<' in markup)
                or (isinstance(markup, str) and not '<' in markup)
        ):
            # Print out warnings for a couple beginner problems
            # involving passing non-markup to Beautiful Soup.
            # Beautiful Soup will still parse the input as markup,
            # just in case that's what the user really wants.
            if (isinstance(markup, str)
                and not os.path.supports_unicode_filenames):
                possible_filename = markup.encode("utf8")
            else:
                possible_filename = markup
            is_file = False
            try:
                is_file = os.path.exists(possible_filename)
            except Exception as e:
                # This is almost certainly a problem involving
                # characters not valid in filenames on this
                # system. Just let it go.
                pass
            if is_file:
                if isinstance(markup, str):
                    markup = markup.encode("utf8")
                warnings.warn(
                    '"%s" looks like a filename, not markup. You should'
                    ' probably open this file and pass the filehandle into'
                    ' Beautiful Soup.' % markup)
            self._check_markup_is_url(markup)
 
        for (self.markup, self.original_encoding, self.declared_html_encoding,
         self.contains_replacement_characters) in (
             self.builder.prepare_markup(
                 markup, from_encoding, exclude_encodings=exclude_encodings)):
            self.reset()
            try:
                self._feed()
                break
            except ParserRejectedMarkup:
                pass
 
        # Clear out the markup and remove the builder's circular
        # reference to this object.
        self.markup = None
        self.builder.soup = None
 
    def __copy__(self):
        copy = type(self)(
            self.encode('utf-8'), builder=self.builder, from_encoding='utf-8'
        )
 
        # Although we encoded the tree to UTF-8, that may not have
        # been the encoding of the original markup. Set the copy's
        # .original_encoding to reflect the original object's
        # .original_encoding.
        copy.original_encoding = self.original_encoding
        return copy
 
    def __getstate__(self):
        # Frequently a tree builder can't be pickled.
        d = dict(self.__dict__)
        if 'builder' in d and not self.builder.picklable:
            d['builder'] = None
        return d
 
    @staticmethod
    def _check_markup_is_url(markup):
        """
        Check if markup looks like it's actually a url and raise a warning
        if so. Markup can be unicode or str (py2) / bytes (py3).
        """
        if isinstance(markup, bytes):
            space = b' '
            cant_start_with = (b"http:", b"https:")
        elif isinstance(markup, str):
            space = ' '
            cant_start_with = ("http:", "https:")
        else:
            return
 
        if any(markup.startswith(prefix) for prefix in cant_start_with):
            if not space in markup:
                if isinstance(markup, bytes):
                    decoded_markup = markup.decode('utf-8', 'replace')
                else:
                    decoded_markup = markup
                warnings.warn(
                    '"%s" looks like a URL. Beautiful Soup is not an'
                    ' HTTP client. You should probably use an HTTP client like'
                    ' requests to get the document behind the URL, and feed'
                    ' that document to Beautiful Soup.' % decoded_markup
                )
 
    def _feed(self):
        # Convert the document to Unicode.
        self.builder.reset()
 
        self.builder.feed(self.markup)
        # Close out any unfinished strings and close all the open tags.
        self.endData()
        while self.currentTag.name != self.ROOT_TAG_NAME:
            self.popTag()
 
    def reset(self):
        Tag.__init__(self, self, self.builder, self.ROOT_TAG_NAME)
        self.hidden = 1
        self.builder.reset()
        self.current_data = []
        self.currentTag = None
        self.tagStack = []
        self.preserve_whitespace_tag_stack = []
        self.pushTag(self)
 
    def new_tag(self, name, namespace=None, nsprefix=None, attrs={}, **kwattrs):
        """Create a new tag associated with this soup."""
        kwattrs.update(attrs)
        return Tag(None, self.builder, name, namespace, nsprefix, kwattrs)
 
    def new_string(self, s, subclass=NavigableString):
        """Create a new NavigableString associated with this soup."""
        return subclass(s)
 
    def insert_before(self, successor):
        raise NotImplementedError("BeautifulSoup objects don't support insert_before().")
 
    def insert_after(self, successor):
        raise NotImplementedError("BeautifulSoup objects don't support insert_after().")
 
    def popTag(self):
        tag = self.tagStack.pop()
        if self.preserve_whitespace_tag_stack and tag == self.preserve_whitespace_tag_stack[-1]:
            self.preserve_whitespace_tag_stack.pop()
        #print "Pop", tag.name
        if self.tagStack:
            self.currentTag = self.tagStack[-1]
        return self.currentTag
 
    def pushTag(self, tag):
        #print "Push", tag.name
        if self.currentTag:
            self.currentTag.contents.append(tag)
        self.tagStack.append(tag)
        self.currentTag = self.tagStack[-1]
        if tag.name in self.builder.preserve_whitespace_tags:
            self.preserve_whitespace_tag_stack.append(tag)
 
    def endData(self, containerClass=NavigableString):
        if self.current_data:
            current_data = ''.join(self.current_data)
            # If whitespace is not preserved, and this string contains
            # nothing but ASCII spaces, replace it with a single space
            # or newline.
            if not self.preserve_whitespace_tag_stack:
                strippable = True
                for i in current_data:
                    if i not in self.ASCII_SPACES:
                        strippable = False
                        break
                if strippable:
                    if '\n' in current_data:
                        current_data = '\n'
                    else:
                        current_data = ' '
 
            # Reset the data collector.
            self.current_data = []
 
            # Should we add this string to the tree at all?
            if self.parse_only and len(self.tagStack) <= 1 and \
                   (not self.parse_only.text or \
                    not self.parse_only.search(current_data)):
                return
 
            o = containerClass(current_data)
            self.object_was_parsed(o)
 
    def object_was_parsed(self, o, parent=None, most_recent_element=None):
        """Add an object to the parse tree."""
        parent = parent or self.currentTag
        previous_element = most_recent_element or self._most_recent_element
 
        next_element = previous_sibling = next_sibling = None
        if isinstance(o, Tag):
            next_element = o.next_element
            next_sibling = o.next_sibling
            previous_sibling = o.previous_sibling
            if not previous_element:
                previous_element = o.previous_element
 
        o.setup(parent, previous_element, next_element, previous_sibling, next_sibling)
 
        self._most_recent_element = o
        parent.contents.append(o)
 
        if parent.next_sibling:
            # This node is being inserted into an element that has
            # already been parsed. Deal with any dangling references.
            index = len(parent.contents)-1
            while index >= 0:
                if parent.contents[index] is o:
                    break
                index -= 1
            else:
                raise ValueError(
                    "Error building tree: supposedly %r was inserted "
                    "into %r after the fact, but I don't see it!" % (
                        o, parent
                    )
                )
            if index == 0:
                previous_element = parent
                previous_sibling = None
            else:
                previous_element = previous_sibling = parent.contents[index-1]
            if index == len(parent.contents)-1:
                next_element = parent.next_sibling
                next_sibling = None
            else:
                next_element = next_sibling = parent.contents[index+1]
 
            o.previous_element = previous_element
            if previous_element:
                previous_element.next_element = o
            o.next_element = next_element
            if next_element:
                next_element.previous_element = o
            o.next_sibling = next_sibling
            if next_sibling:
                next_sibling.previous_sibling = o
            o.previous_sibling = previous_sibling
            if previous_sibling:
                previous_sibling.next_sibling = o
 
    def _popToTag(self, name, nsprefix=None, inclusivePop=True):
        """Pops the tag stack up to and including the most recent
        instance of the given tag. If inclusivePop is false, pops the tag
        stack up to but *not* including the most recent instqance of
        the given tag."""
        #print "Popping to %s" % name
        if name == self.ROOT_TAG_NAME:
            # The BeautifulSoup object itself can never be popped.
            return
 
        most_recently_popped = None
 
        stack_size = len(self.tagStack)
        for i in range(stack_size - 1, 0, -1):
            t = self.tagStack[i]
            if (name == t.name and nsprefix == t.prefix):
                if inclusivePop:
                    most_recently_popped = self.popTag()
                break
            most_recently_popped = self.popTag()
 
        return most_recently_popped
 
    def handle_starttag(self, name, namespace, nsprefix, attrs):
        """Push a start tag on to the stack.
 
        If this method returns None, the tag was rejected by the
        SoupStrainer. You should proceed as if the tag had not occurred
        in the document. For instance, if this was a self-closing tag,
        don't call handle_endtag.
        """
 
        # print "Start tag %s: %s" % (name, attrs)
        self.endData()
 
        if (self.parse_only and len(self.tagStack) <= 1
            and (self.parse_only.text
                 or not self.parse_only.search_tag(name, attrs))):
            return None
 
        tag = Tag(self, self.builder, name, namespace, nsprefix, attrs,
                  self.currentTag, self._most_recent_element)
        if tag is None:
            return tag
        if self._most_recent_element:
            self._most_recent_element.next_element = tag
        self._most_recent_element = tag
        self.pushTag(tag)
        return tag
 
    def handle_endtag(self, name, nsprefix=None):
        #print "End tag: " + name
        self.endData()
        self._popToTag(name, nsprefix)
 
    def handle_data(self, data):
        self.current_data.append(data)
 
    def decode(self, pretty_print=False,
               eventual_encoding=DEFAULT_OUTPUT_ENCODING,
               formatter="minimal"):
        """Returns a string or Unicode representation of this document.
        To get Unicode, pass None for encoding."""
 
        if self.is_xml:
            # Print the XML declaration
            encoding_part = ''
            if eventual_encoding != None:
                encoding_part = ' encoding="%s"' % eventual_encoding
            prefix = '<?xml version="1.0"%s?>\n' % encoding_part
        else:
            prefix = ''
        if not pretty_print:
            indent_level = None
        else:
            indent_level = 0
        return prefix + super(BeautifulSoup, self).decode(
            indent_level, eventual_encoding, formatter)
 
# Alias to make it easier to type import: 'from bs4 import _soup'
_s = BeautifulSoup
_soup = BeautifulSoup
 
class BeautifulStoneSoup(BeautifulSoup):
    """Deprecated interface to an XML parser."""
 
    def __init__(self, *args, **kwargs):
        kwargs['features'] = 'xml'
        warnings.warn(
            'The BeautifulStoneSoup class is deprecated. Instead of using '
            'it, pass features="xml" into the BeautifulSoup constructor.')
        super(BeautifulStoneSoup, self).__init__(*args, **kwargs)
 
class StopParsing(Exception):
    pass
 
class FeatureNotFound(ValueError):
    pass
 
#By default, act as an HTML pretty-printer.
if __name__ == '__main__':
    import sys
    soup = BeautifulSoup(sys.stdin)
    print(soup.prettify())

find_all（）源码：

# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
__license__ = "MIT"
 
try:
    from collections.abc import Callable # Python 3.6
except ImportError as e:
    from collections import Callable
import re
import shlex
import sys
import warnings
from bs4.dammit import EntitySubstitution
 
DEFAULT_OUTPUT_ENCODING = "utf-8"
PY3K = (sys.version_info[0] > 2)
 
whitespace_re = re.compile(r"\s+")
 
def _alias(attr):
    """Alias one attribute name to another for backward compatibility"""
    @property
    def alias(self):
        return getattr(self, attr)
 
    @alias.setter
    def alias(self):
        return setattr(self, attr)
    return alias
 
class NamespacedAttribute(str):
 
    def __new__(cls, prefix, name, namespace=None):
        if name is None:
            obj = str.__new__(cls, prefix)
        elif prefix is None:
            # Not really namespaced.
            obj = str.__new__(cls, name)
        else:
            obj = str.__new__(cls, prefix + ":" + name)
        obj.prefix = prefix
        obj.name = name
        obj.namespace = namespace
        return obj
 
class AttributeValueWithCharsetSubstitution(str):
    """A stand-in object for a character encoding specified in HTML."""
 
class CharsetMetaAttributeValue(AttributeValueWithCharsetSubstitution):
    """A generic stand-in for the value of a meta tag's 'charset' attribute.
 
    When Beautiful Soup parses the markup '<meta charset="utf8">', the
    value of the 'charset' attribute will be one of these objects.
    """
 
    def __new__(cls, original_value):
        obj = str.__new__(cls, original_value)
        obj.original_value = original_value
        return obj
 
    def encode(self, encoding):
        return encoding
 
class ContentMetaAttributeValue(AttributeValueWithCharsetSubstitution):
    """A generic stand-in for the value of a meta tag's 'content' attribute.
 
    When Beautiful Soup parses the markup:
     <meta http-equiv="content-type" content="text/html; charset=utf8">
 
    The value of the 'content' attribute will be one of these objects.
    """
 
    CHARSET_RE = re.compile(r"((^|;)\s*charset=)([^;]*)", re.M)
 
    def __new__(cls, original_value):
        match = cls.CHARSET_RE.search(original_value)
        if match is None:
            # No substitution necessary.
            return str.__new__(str, original_value)
 
        obj = str.__new__(cls, original_value)
        obj.original_value = original_value
        return obj
 
    def encode(self, encoding):
        def rewrite(match):
            return match.group(1) + encoding
        return self.CHARSET_RE.sub(rewrite, self.original_value)
 
class HTMLAwareEntitySubstitution(EntitySubstitution):
 
    """Entity substitution rules that are aware of some HTML quirks.
 
    Specifically, the contents of <script> and <style> tags should not
    undergo entity substitution.
 
    Incoming NavigableString objects are checked to see if they're the
    direct children of a <script> or <style> tag.
    """
 
    cdata_containing_tags = set(["script", "style"])
 
    preformatted_tags = set(["pre"])
 
    preserve_whitespace_tags = set(['pre', 'textarea'])
 
    @classmethod
    def _substitute_if_appropriate(cls, ns, f):
        if (isinstance(ns, NavigableString)
            and ns.parent is not None
            and ns.parent.name in cls.cdata_containing_tags):
            # Do nothing.
            return ns
        # Substitute.
        return f(ns)
 
    @classmethod
    def substitute_html(cls, ns):
        return cls._substitute_if_appropriate(
            ns, EntitySubstitution.substitute_html)
 
    @classmethod
    def substitute_xml(cls, ns):
        return cls._substitute_if_appropriate(
            ns, EntitySubstitution.substitute_xml)
 
class Formatter(object):
    """Contains information about how to format a parse tree."""
 
    # By default, represent void elements as <tag/> rather than <tag>
    void_element_close_prefix = '/'
 
    def substitute_entities(self, *args, **kwargs):
        """Transform certain characters into named entities."""
        raise NotImplementedError()
 
class HTMLFormatter(Formatter):
    """The default HTML formatter."""
    def substitute(self, *args, **kwargs):
        return HTMLAwareEntitySubstitution.substitute_html(*args, **kwargs)
 
class MinimalHTMLFormatter(Formatter):
    """A minimal HTML formatter."""
    def substitute(self, *args, **kwargs):
        return HTMLAwareEntitySubstitution.substitute_xml(*args, **kwargs)
 
class HTML5Formatter(HTMLFormatter):
    """An HTML formatter that omits the slash in a void tag."""
    void_element_close_prefix = None
 
class XMLFormatter(Formatter):
    """Substitute only the essential XML entities."""
    def substitute(self, *args, **kwargs):
        return EntitySubstitution.substitute_xml(*args, **kwargs)
 
class HTMLXMLFormatter(Formatter):
    """Format XML using HTML rules."""
    def substitute(self, *args, **kwargs):
        return HTMLAwareEntitySubstitution.substitute_html(*args, **kwargs)
 
class PageElement(object):
    """Contains the navigational information for some part of the page
    (either a tag or a piece of text)"""
 
    # There are five possible values for the "formatter" argument passed in
    # to methods like encode() and prettify():
    #
    # "html" - All Unicode characters with corresponding HTML entities
    #   are converted to those entities on output.
    # "html5" - The same as "html", but empty void tags are represented as
    #   <tag> rather than <tag/>
    # "minimal" - Bare ampersands and angle brackets are converted to
    #   XML entities: &amp; &lt; &gt;
    # None - The null formatter. Unicode characters are never
    #   converted to entities.  This is not recommended, but it's
    #   faster than "minimal".
    # A callable function - it will be called on every string that needs to undergo entity substitution.
    # A Formatter instance - Formatter.substitute(string) will be called on every string that
    #  needs to undergo entity substitution.
    #
 
    # In an HTML document, the default "html", "html5", and "minimal"
    # functions will leave the contents of <script> and <style> tags
    # alone. For an XML document, all tags will be given the same
    # treatment.
 
    HTML_FORMATTERS = {
        "html" : HTMLFormatter(),
        "html5" : HTML5Formatter(),
        "minimal" : MinimalHTMLFormatter(),
        None : None
        }
 
    XML_FORMATTERS = {
        "html" : HTMLXMLFormatter(),
        "minimal" : XMLFormatter(),
        None : None
        }
 
    def format_string(self, s, formatter='minimal'):
        """Format the given string using the given formatter."""
        if isinstance(formatter, str):
            formatter = self._formatter_for_name(formatter)
        if formatter is None:
            output = s
        else:
            if callable(formatter):
                # Backwards compatibility -- you used to pass in a formatting method.
                output = formatter(s)
            else:
                output = formatter.substitute(s)
        return output
 
    @property
    def _is_xml(self):
        """Is this element part of an XML tree or an HTML tree?
 
        This is used when mapping a formatter name ("minimal") to an
        appropriate function (one that performs entity-substitution on
        the contents of <script> and <style> tags, or not). It can be
        inefficient, but it should be called very rarely.
        """
        if self.known_xml is not None:
            # Most of the time we will have determined this when the
            # document is parsed.
            return self.known_xml
 
        # Otherwise, it's likely that this element was created by
        # direct invocation of the constructor from within the user's
        # Python code.
        if self.parent is None:
            # This is the top-level object. It should have .known_xml set
            # from tree creation. If not, take a guess--BS is usually
            # used on HTML markup.
            return getattr(self, 'is_xml', False)
        return self.parent._is_xml
 
    def _formatter_for_name(self, name):
        "Look up a formatter function based on its name and the tree."
        if self._is_xml:
            return self.XML_FORMATTERS.get(name, XMLFormatter())
        else:
            return self.HTML_FORMATTERS.get(name, HTMLFormatter())
 
    def setup(self, parent=None, previous_element=None, next_element=None,
              previous_sibling=None, next_sibling=None):
        """Sets up the initial relations between this element and
        other elements."""
        self.parent = parent
 
        self.previous_element = previous_element
        if previous_element is not None:
            self.previous_element.next_element = self
 
        self.next_element = next_element
        if self.next_element:
            self.next_element.previous_element = self
 
        self.next_sibling = next_sibling
        if self.next_sibling:
            self.next_sibling.previous_sibling = self
 
        if (not previous_sibling
            and self.parent is not None and self.parent.contents):
            previous_sibling = self.parent.contents[-1]
 
        self.previous_sibling = previous_sibling
        if previous_sibling:
            self.previous_sibling.next_sibling = self
 
    nextSibling = _alias("next_sibling")  # BS3
    previousSibling = _alias("previous_sibling")  # BS3
 
    def replace_with(self, replace_with):
        if not self.parent:
            raise ValueError(
                "Cannot replace one element with another when the"
                "element to be replaced is not part of a tree.")
        if replace_with is self:
            return
        if replace_with is self.parent:
            raise ValueError("Cannot replace a Tag with its parent.")
        old_parent = self.parent
        my_index = self.parent.index(self)
        self.extract()
        old_parent.insert(my_index, replace_with)
        return self
    replaceWith = replace_with  # BS3
 
    def unwrap(self):
        my_parent = self.parent
        if not self.parent:
            raise ValueError(
                "Cannot replace an element with its contents when that"
                "element is not part of a tree.")
        my_index = self.parent.index(self)
        self.extract()
        for child in reversed(self.contents[:]):
            my_parent.insert(my_index, child)
        return self
    replace_with_children = unwrap
    replaceWithChildren = unwrap  # BS3
 
    def wrap(self, wrap_inside):
        me = self.replace_with(wrap_inside)
        wrap_inside.append(me)
        return wrap_inside
 
    def extract(self):
        """Destructively rips this element out of the tree."""
        if self.parent is not None:
            del self.parent.contents[self.parent.index(self)]
 
        #Find the two elements that would be next to each other if
        #this element (and any children) hadn't been parsed. Connect
        #the two.
        last_child = self._last_descendant()
        next_element = last_child.next_element
 
        if (self.previous_element is not None and
            self.previous_element is not next_element):
            self.previous_element.next_element = next_element
        if next_element is not None and next_element is not self.previous_element:
            next_element.previous_element = self.previous_element
        self.previous_element = None
        last_child.next_element = None
 
        self.parent = None
        if (self.previous_sibling is not None
            and self.previous_sibling is not self.next_sibling):
            self.previous_sibling.next_sibling = self.next_sibling
        if (self.next_sibling is not None
            and self.next_sibling is not self.previous_sibling):
            self.next_sibling.previous_sibling = self.previous_sibling
        self.previous_sibling = self.next_sibling = None
        return self
 
    def _last_descendant(self, is_initialized=True, accept_self=True):
        "Finds the last element beneath this object to be parsed."
        if is_initialized and self.next_sibling:
            last_child = self.next_sibling.previous_element
        else:
            last_child = self
            while isinstance(last_child, Tag) and last_child.contents:
                last_child = last_child.contents[-1]
        if not accept_self and last_child is self:
            last_child = None
        return last_child
    # BS3: Not part of the API!
    _lastRecursiveChild = _last_descendant
 
    def insert(self, position, new_child):
        if new_child is None:
            raise ValueError("Cannot insert None into a tag.")
        if new_child is self:
            raise ValueError("Cannot insert a tag into itself.")
        if (isinstance(new_child, str)
            and not isinstance(new_child, NavigableString)):
            new_child = NavigableString(new_child)
 
        from bs4 import BeautifulSoup
        if isinstance(new_child, BeautifulSoup):
            # We don't want to end up with a situation where one BeautifulSoup
            # object contains another. Insert the children one at a time.
            for subchild in list(new_child.contents):
                self.insert(position, subchild)
                position += 1
            return
        position = min(position, len(self.contents))
        if hasattr(new_child, 'parent') and new_child.parent is not None:
            # We're 'inserting' an element that's already one
            # of this object's children.
            if new_child.parent is self:
                current_index = self.index(new_child)
                if current_index < position:
                    # We're moving this element further down the list
                    # of this object's children. That means that when
                    # we extract this element, our target index will
                    # jump down one.
                    position -= 1
            new_child.extract()
 
        new_child.parent = self
        previous_child = None
        if position == 0:
            new_child.previous_sibling = None
            new_child.previous_element = self
        else:
            previous_child = self.contents[position - 1]
            new_child.previous_sibling = previous_child
            new_child.previous_sibling.next_sibling = new_child
            new_child.previous_element = previous_child._last_descendant(False)
        if new_child.previous_element is not None:
            new_child.previous_element.next_element = new_child
 
        new_childs_last_element = new_child._last_descendant(False)
 
        if position >= len(self.contents):
            new_child.next_sibling = None
 
            parent = self
            parents_next_sibling = None
            while parents_next_sibling is None and parent is not None:
                parents_next_sibling = parent.next_sibling
                parent = parent.parent
                if parents_next_sibling is not None:
                    # We found the element that comes next in the document.
                    break
            if parents_next_sibling is not None:
                new_childs_last_element.next_element = parents_next_sibling
            else:
                # The last element of this tag is the last element in
                # the document.
                new_childs_last_element.next_element = None
        else:
            next_child = self.contents[position]
            new_child.next_sibling = next_child
            if new_child.next_sibling is not None:
                new_child.next_sibling.previous_sibling = new_child
            new_childs_last_element.next_element = next_child
 
        if new_childs_last_element.next_element is not None:
            new_childs_last_element.next_element.previous_element = new_childs_last_element
        self.contents.insert(position, new_child)
 
    def append(self, tag):
        """Appends the given tag to the contents of this tag."""
        self.insert(len(self.contents), tag)
 
    def insert_before(self, predecessor):
        """Makes the given element the immediate predecessor of this one.
 
        The two elements will have the same parent, and the given element
        will be immediately before this one.
        """
        if self is predecessor:
            raise ValueError("Can't insert an element before itself.")
        parent = self.parent
        if parent is None:
            raise ValueError(
                "Element has no parent, so 'before' has no meaning.")
        # Extract first so that the index won't be screwed up if they
        # are siblings.
        if isinstance(predecessor, PageElement):
            predecessor.extract()
        index = parent.index(self)
        parent.insert(index, predecessor)
 
    def insert_after(self, successor):
        """Makes the given element the immediate successor of this one.
 
        The two elements will have the same parent, and the given element
        will be immediately after this one.
        """
        if self is successor:
            raise ValueError("Can't insert an element after itself.")
        parent = self.parent
        if parent is None:
            raise ValueError(
                "Element has no parent, so 'after' has no meaning.")
        # Extract first so that the index won't be screwed up if they
        # are siblings.
        if isinstance(successor, PageElement):
            successor.extract()
        index = parent.index(self)
        parent.insert(index+1, successor)
 
    def find_next(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the first item that matches the given criteria and
        appears after this Tag in the document."""
        return self._find_one(self.find_all_next, name, attrs, text, **kwargs)
    findNext = find_next  # BS3
 
    def find_all_next(self, name=None, attrs={}, text=None, limit=None,
                    **kwargs):
        """Returns all items that match the given criteria and appear
        after this Tag in the document."""
        return self._find_all(name, attrs, text, limit, self.next_elements,
                             **kwargs)
    findAllNext = find_all_next  # BS3
 
    def find_next_sibling(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the closest sibling to this Tag that matches the
        given criteria and appears after this Tag in the document."""
        return self._find_one(self.find_next_siblings, name, attrs, text,
                             **kwargs)
    findNextSibling = find_next_sibling  # BS3
 
    def find_next_siblings(self, name=None, attrs={}, text=None, limit=None,
                           **kwargs):
        """Returns the siblings of this Tag that match the given
        criteria and appear after this Tag in the document."""
        return self._find_all(name, attrs, text, limit,
                              self.next_siblings, **kwargs)
    findNextSiblings = find_next_siblings   # BS3
    fetchNextSiblings = find_next_siblings  # BS2
 
    def find_previous(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the first item that matches the given criteria and
        appears before this Tag in the document."""
        return self._find_one(
            self.find_all_previous, name, attrs, text, **kwargs)
    findPrevious = find_previous  # BS3
 
    def find_all_previous(self, name=None, attrs={}, text=None, limit=None,
                        **kwargs):
        """Returns all items that match the given criteria and appear
        before this Tag in the document."""
        return self._find_all(name, attrs, text, limit, self.previous_elements,
                           **kwargs)
    findAllPrevious = find_all_previous  # BS3
    fetchPrevious = find_all_previous    # BS2
 
    def find_previous_sibling(self, name=None, attrs={}, text=None, **kwargs):
        """Returns the closest sibling to this Tag that matches the
        given criteria and appears before this Tag in the document."""
        return self._find_one(self.find_previous_siblings, name, attrs, text,
                             **kwargs)
    findPreviousSibling = find_previous_sibling  # BS3
 
    def find_previous_siblings(self, name=None, attrs={}, text=None,
                               limit=None, **kwargs):
        """Returns the siblings of this Tag that match the given
        criteria and appear before this Tag in the document."""
        return self._find_all(name, attrs, text, limit,
                              self.previous_siblings, **kwargs)
    findPreviousSiblings = find_previous_siblings   # BS3
    fetchPreviousSiblings = find_previous_siblings  # BS2
 
    def find_parent(self, name=None, attrs={}, **kwargs):
        """Returns the closest parent of this Tag that matches the given
        criteria."""
        # NOTE: We can't use _find_one because findParents takes a different
        # set of arguments.
        r = None
        l = self.find_parents(name, attrs, 1, **kwargs)
        if l:
            r = l[0]
        return r
    findParent = find_parent  # BS3
 
    def find_parents(self, name=None, attrs={}, limit=None, **kwargs):
        """Returns the parents of this Tag that match the given
        criteria."""
 
        return self._find_all(name, attrs, None, limit, self.parents,
                             **kwargs)
    findParents = find_parents   # BS3
    fetchParents = find_parents  # BS2
 
    @property
    def next(self):
        return self.next_element
 
    @property
    def previous(self):
        return self.previous_element
 
    #These methods do the real heavy lifting.
 
    def _find_one(self, method, name, attrs, text, **kwargs):
        r = None
        l = method(name, attrs, text, 1, **kwargs)
        if l:
            r = l[0]
        return r
 
    def _find_all(self, name, attrs, text, limit, generator, **kwargs):
        "Iterates over a generator looking for things that match."
 
        if text is None and 'string' in kwargs:
            text = kwargs['string']
            del kwargs['string']
 
        if isinstance(name, SoupStrainer):
            strainer = name
        else:
            strainer = SoupStrainer(name, attrs, text, **kwargs)
 
        if text is None and not limit and not attrs and not kwargs:
            if name is True or name is None:
                # Optimization to find all tags.
                result = (element for element in generator
                          if isinstance(element, Tag))
                return ResultSet(strainer, result)
            elif isinstance(name, str):
                # Optimization to find all tags with a given name.
                if name.count(':') == 1:
                    # This is a name with a prefix. If this is a namespace-aware document,
                    # we need to match the local name against tag.name. If not,
                    # we need to match the fully-qualified name against tag.name.
                    prefix, local_name = name.split(':', 1)
                else:
                    prefix = None
                    local_name = name
                result = (element for element in generator
                          if isinstance(element, Tag)
                          and (
                              element.name == name
                          ) or (
                              element.name == local_name
                              and (prefix is None or element.prefix == prefix)
                          )
                )
                return ResultSet(strainer, result)
        results = ResultSet(strainer)
        while True:
            try:
                i = next(generator)
            except StopIteration:
                break
            if i:
                found = strainer.search(i)
                if found:
                    results.append(found)
                    if limit and len(results) >= limit:
                        break
        return results
 
    #These generators can be used to navigate starting from both
    #NavigableStrings and Tags.
    @property
    def next_elements(self):
        i = self.next_element
        while i is not None:
            yield i
            i = i.next_element
 
    @property
    def next_siblings(self):
        i = self.next_sibling
        while i is not None:
            yield i
            i = i.next_sibling
 
    @property
    def previous_elements(self):
        i = self.previous_element
        while i is not None:
            yield i
            i = i.previous_element
 
    @property
    def previous_siblings(self):
        i = self.previous_sibling
        while i is not None:
            yield i
            i = i.previous_sibling
 
    @property
    def parents(self):
        i = self.parent
        while i is not None:
            yield i
            i = i.parent
 
    # Methods for supporting CSS selectors.
 
    tag_name_re = re.compile('^[a-zA-Z0-9][-.a-zA-Z0-9:_]*$')
 
    # /^([a-zA-Z0-9][-.a-zA-Z0-9:_]*)\[(\w+)([=~\|\^\$\*]?)=?"?([^\]"]*)"?\]$/
    #   \---------------------------/  \---/\-------------/    \-------/
    #     |                              |         |               |
    #     |                              |         |           The value
    #     |                              |    ~,|,^,$,* or =
    #     |                           Attribute
    #    Tag
    attribselect_re = re.compile(
        r'^(?P<tag>[a-zA-Z0-9][-.a-zA-Z0-9:_]*)?\[(?P<attribute>[\w-]+)(?P<operator>[=~\|\^\$\*]?)' +
        r'=?"?(?P<value>[^\]"]*)"?\]$'
        )
 
    def _attr_value_as_string(self, value, default=None):
        """Force an attribute value into a string representation.
 
        A multi-valued attribute will be converted into a
        space-separated stirng.
        """
        value = self.get(value, default)
        if isinstance(value, list) or isinstance(value, tuple):
            value =" ".join(value)
        return value
 
    def _tag_name_matches_and(self, function, tag_name):
        if not tag_name:
            return function
        else:
            def _match(tag):
                return tag.name == tag_name and function(tag)
            return _match
 
    def _attribute_checker(self, operator, attribute, value=''):
        """Create a function that performs a CSS selector operation.
 
        Takes an operator, attribute and optional value. Returns a
        function that will return True for elements that match that
        combination.
        """
        if operator == '=':
            # string representation of `attribute` is equal to `value`
            return lambda el: el._attr_value_as_string(attribute) == value
        elif operator == '~':
            # space-separated list representation of `attribute`
            # contains `value`
            def _includes_value(element):
                attribute_value = element.get(attribute, [])
                if not isinstance(attribute_value, list):
                    attribute_value = attribute_value.split()
                return value in attribute_value
            return _includes_value
        elif operator == '^':
            # string representation of `attribute` starts with `value`
            return lambda el: el._attr_value_as_string(
                attribute, '').startswith(value)
        elif operator == '$':
            # string representation of `attribute` ends with `value`
            return lambda el: el._attr_value_as_string(
                attribute, '').endswith(value)
        elif operator == '*':
            # string representation of `attribute` contains `value`
            return lambda el: value in el._attr_value_as_string(attribute, '')
        elif operator == '|':
            # string representation of `attribute` is either exactly
            # `value` or starts with `value` and then a dash.
            def _is_or_starts_with_dash(element):
                attribute_value = element._attr_value_as_string(attribute, '')
                return (attribute_value == value or attribute_value.startswith(
                        value + '-'))
            return _is_or_starts_with_dash
        else:
            return lambda el: el.has_attr(attribute)
 
    # Old non-property versions of the generators, for backwards
    # compatibility with BS3.
    def nextGenerator(self):
        return self.next_elements
 
    def nextSiblingGenerator(self):
        return self.next_siblings
 
    def previousGenerator(self):
        return self.previous_elements
 
    def previousSiblingGenerator(self):
        return self.previous_siblings
 
    def parentGenerator(self):
        return self.parents
 
class NavigableString(str, PageElement):
 
    PREFIX = ''
    SUFFIX = ''
 
    # We can't tell just by looking at a string whether it's contained
    # in an XML document or an HTML document.
 
    known_xml = None
 
    def __new__(cls, value):
        """Create a new NavigableString.
 
        When unpickling a NavigableString, this method is called with
        the string in DEFAULT_OUTPUT_ENCODING. That encoding needs to be
        passed in to the superclass's __new__ or the superclass won't know
        how to handle non-ASCII characters.
        """
        if isinstance(value, str):
            u = str.__new__(cls, value)
        else:
            u = str.__new__(cls, value, DEFAULT_OUTPUT_ENCODING)
        u.setup()
        return u
 
    def __copy__(self):
        """A copy of a NavigableString has the same contents and class
        as the original, but it is not connected to the parse tree.
        """
        return type(self)(self)
 
    def __getnewargs__(self):
        return (str(self),)
 
    def __getattr__(self, attr):
        """text.string gives you text. This is for backwards
        compatibility for Navigable*String, but for CData* it lets you
        get the string without the CData wrapper."""
        if attr == 'string':
            return self
        else:
            raise AttributeError(
                "'%s' object has no attribute '%s'" % (
                    self.__class__.__name__, attr))
 
    def output_ready(self, formatter="minimal"):
        output = self.format_string(self, formatter)
        return self.PREFIX + output + self.SUFFIX
 
    @property
    def name(self):
        return None
 
    @name.setter
    def name(self, name):
        raise AttributeError("A NavigableString cannot be given a name.")
 
class PreformattedString(NavigableString):
    """A NavigableString not subject to the normal formatting rules.
 
    The string will be passed into the formatter (to trigger side effects),
    but the return value will be ignored.
    """
 
    def output_ready(self, formatter="minimal"):
        """CData strings are passed into the formatter.
        But the return value is ignored."""
        self.format_string(self, formatter)
        return self.PREFIX + self + self.SUFFIX
 
class CData(PreformattedString):
 
    PREFIX = '<![CDATA['
    SUFFIX = ']]>'
 
class ProcessingInstruction(PreformattedString):
    """A SGML processing instruction."""
 
    PREFIX = '<?'
    SUFFIX = '>'
 
class XMLProcessingInstruction(ProcessingInstruction):
    """An XML processing instruction."""
    PREFIX = '<?'
    SUFFIX = '?>'
 
class Comment(PreformattedString):
 
    PREFIX = '<!--'
    SUFFIX = '-->'
 
class Declaration(PreformattedString):
    PREFIX = '<?'
    SUFFIX = '?>'
 
class Doctype(PreformattedString):
 
    @classmethod
    def for_name_and_ids(cls, name, pub_id, system_id):
        value = name or ''
        if pub_id is not None:
            value += ' PUBLIC "%s"' % pub_id
            if system_id is not None:
                value += ' "%s"' % system_id
        elif system_id is not None:
            value += ' SYSTEM "%s"' % system_id
 
        return Doctype(value)
 
    PREFIX = '<!DOCTYPE '
    SUFFIX = '>\n'
 
class Tag(PageElement):
 
    """Represents a found HTML tag with its attributes and contents."""
 
    def __init__(self, parser=None, builder=None, name=None, namespace=None,
                 prefix=None, attrs=None, parent=None, previous=None,
                 is_xml=None):
        "Basic constructor."
 
        if parser is None:
            self.parser_class = None
        else:
            # We don't actually store the parser object: that lets extracted
            # chunks be garbage-collected.
            self.parser_class = parser.__class__
        if name is None:
            raise ValueError("No value provided for new tag's name.")
        self.name = name
        self.namespace = namespace
        self.prefix = prefix
        if builder is not None:
            preserve_whitespace_tags = builder.preserve_whitespace_tags
        else:
            if is_xml:
                preserve_whitespace_tags = []
            else:
                preserve_whitespace_tags = HTMLAwareEntitySubstitution.preserve_whitespace_tags
        self.preserve_whitespace_tags = preserve_whitespace_tags
        if attrs is None:
            attrs = {}
        elif attrs:
            if builder is not None and builder.cdata_list_attributes:
                attrs = builder._replace_cdata_list_attribute_values(
                    self.name, attrs)
            else:
                attrs = dict(attrs)
        else:
            attrs = dict(attrs)
 
        # If possible, determine ahead of time whether this tag is an
        # XML tag.
        if builder:
            self.known_xml = builder.is_xml
        else:
            self.known_xml = is_xml
        self.attrs = attrs
        self.contents = []
        self.setup(parent, previous)
        self.hidden = False
 
        # Set up any substitutions, such as the charset in a META tag.
        if builder is not None:
            builder.set_up_substitutions(self)
            self.can_be_empty_element = builder.can_be_empty_element(name)
        else:
            self.can_be_empty_element = False
 
    parserClass = _alias("parser_class")  # BS3
 
    def __copy__(self):
        """A copy of a Tag is a new Tag, unconnected to the parse tree.
        Its contents are a copy of the old Tag's contents.
        """
        clone = type(self)(None, self.builder, self.name, self.namespace,
                           self.prefix, self.attrs, is_xml=self._is_xml)
        for attr in ('can_be_empty_element', 'hidden'):
            setattr(clone, attr, getattr(self, attr))
        for child in self.contents:
            clone.append(child.__copy__())
        return clone
 
    @property
    def is_empty_element(self):
        """Is this tag an empty-element tag? (aka a self-closing tag)
 
        A tag that has contents is never an empty-element tag.
 
        A tag that has no contents may or may not be an empty-element
        tag. It depends on the builder used to create the tag. If the
        builder has a designated list of empty-element tags, then only
        a tag whose name shows up in that list is considered an
        empty-element tag.
 
        If the builder has no designated list of empty-element tags,
        then any tag with no contents is an empty-element tag.
        """
        return len(self.contents) == 0 and self.can_be_empty_element
    isSelfClosing = is_empty_element  # BS3
 
    @property
    def string(self):
        """Convenience property to get the single string within this tag.
 
        :Return: If this tag has a single string child, return value
         is that string. If this tag has no children, or more than one
         child, return value is None. If this tag has one child tag,
         return value is the 'string' attribute of the child tag,
         recursively.
        """
        if len(self.contents) != 1:
            return None
        child = self.contents[0]
        if isinstance(child, NavigableString):
            return child
        return child.string
 
    @string.setter
    def string(self, string):
        self.clear()
        self.append(string.__class__(string))
 
    def _all_strings(self, strip=False, types=(NavigableString, CData)):
        """Yield all strings of certain classes, possibly stripping them.
 
        By default, yields only NavigableString and CData objects. So
        no comments, processing instructions, etc.
        """
        for descendant in self.descendants:
            if (
                (types is None and not isinstance(descendant, NavigableString))
                or
                (types is not None and type(descendant) not in types)):
                continue
            if strip:
                descendant = descendant.strip()
                if len(descendant) == 0:
                    continue
            yield descendant
 
    strings = property(_all_strings)
 
    @property
    def stripped_strings(self):
        for string in self._all_strings(True):
            yield string
 
    def get_text(self, separator="", strip=False,
                 types=(NavigableString, CData)):
        """
        Get all child strings, concatenated using the given separator.
        """
        return separator.join([s for s in self._all_strings(
                    strip, types=types)])
    getText = get_text
    text = property(get_text)
 
    def decompose(self):
        """Recursively destroys the contents of this tree."""
        self.extract()
        i = self
        while i is not None:
            next = i.next_element
            i.__dict__.clear()
            i.contents = []
            i = next
 
    def clear(self, decompose=False):
        """
        Extract all children. If decompose is True, decompose instead.
        """
        if decompose:
            for element in self.contents[:]:
                if isinstance(element, Tag):
                    element.decompose()
                else:
                    element.extract()
        else:
            for element in self.contents[:]:
                element.extract()
 
    def index(self, element):
        """
        Find the index of a child by identity, not value. Avoids issues with
        tag.contents.index(element) getting the index of equal elements.
        """
        for i, child in enumerate(self.contents):
            if child is element:
                return i
        raise ValueError("Tag.index: element not in tag")
 
    def get(self, key, default=None):
        """Returns the value of the 'key' attribute for the tag, or
        the value given for 'default' if it doesn't have that
        attribute."""
        return self.attrs.get(key, default)
 
    def get_attribute_list(self, key, default=None):
        """The same as get(), but always returns a list."""
        value = self.get(key, default)
        if not isinstance(value, list):
            value = [value]
        return value
 
    def has_attr(self, key):
        return key in self.attrs
 
    def __hash__(self):
        return str(self).__hash__()
 
    def __getitem__(self, key):
        """tag[key] returns the value of the 'key' attribute for the tag,
        and throws an exception if it's not there."""
        return self.attrs[key]
 
    def __iter__(self):
        "Iterating over a tag iterates over its contents."
        return iter(self.contents)
 
    def __len__(self):
        "The length of a tag is the length of its list of contents."
        return len(self.contents)
 
    def __contains__(self, x):
        return x in self.contents
 
    def __bool__(self):
        "A tag is non-None even if it has no contents."
        return True
 
    def __setitem__(self, key, value):
        """Setting tag[key] sets the value of the 'key' attribute for the
        tag."""
        self.attrs[key] = value
 
    def __delitem__(self, key):
        "Deleting tag[key] deletes all 'key' attributes for the tag."
        self.attrs.pop(key, None)
 
    def __call__(self, *args, **kwargs):
        """Calling a tag like a function is the same as calling its
        find_all() method. Eg. tag('a') returns a list of all the A tags
        found within this tag."""
        return self.find_all(*args, **kwargs)
 
    def __getattr__(self, tag):
        #print "Getattr %s.%s" % (self.__class__, tag)
        if len(tag) > 3 and tag.endswith('Tag'):
            # BS3: soup.aTag -> "soup.find("a")
            tag_name = tag[:-3]
            warnings.warn(
                '.%(name)sTag is deprecated, use .find("%(name)s") instead. If you really were looking for a tag called %(name)sTag, use .find("%(name)sTag")' % dict(
                    name=tag_name
                )
            )
            return self.find(tag_name)
        # We special case contents to avoid recursion.
        elif not tag.startswith("__") and not tag == "contents":
            return self.find(tag)
        raise AttributeError(
            "'%s' object has no attribute '%s'" % (self.__class__, tag))
 
    def __eq__(self, other):
        """Returns true iff this tag has the same name, the same attributes,
        and the same contents (recursively) as the given tag."""
        if self is other:
            return True
        if (not hasattr(other, 'name') or
            not hasattr(other, 'attrs') or
            not hasattr(other, 'contents') or
            self.name != other.name or
            self.attrs != other.attrs or
            len(self) != len(other)):
            return False
        for i, my_child in enumerate(self.contents):
            if my_child != other.contents[i]:
                return False
        return True
 
    def __ne__(self, other):
        """Returns true iff this tag is not identical to the other tag,
        as defined in __eq__."""
        return not self == other
 
    def __repr__(self, encoding="unicode-escape"):
        """Renders this tag as a string."""
        if PY3K:
            # "The return value must be a string object", i.e. Unicode
            return self.decode()
        else:
            # "The return value must be a string object", i.e. a bytestring.
            # By convention, the return value of __repr__ should also be
            # an ASCII string.
            return self.encode(encoding)
 
    def __unicode__(self):
        return self.decode()
 
    def __str__(self):
        if PY3K:
            return self.decode()
        else:
            return self.encode()
 
    if PY3K:
        __str__ = __repr__ = __unicode__
 
    def encode(self, encoding=DEFAULT_OUTPUT_ENCODING,
               indent_level=None, formatter="minimal",
               errors="xmlcharrefreplace"):
        # Turn the data structure into Unicode, then encode the
        # Unicode.
        u = self.decode(indent_level, encoding, formatter)
        return u.encode(encoding, errors)
 
    def _should_pretty_print(self, indent_level):
        """Should this tag be pretty-printed?"""
 
        return (
            indent_level is not None
            and self.name not in self.preserve_whitespace_tags
        )
 
    def decode(self, indent_level=None,
               eventual_encoding=DEFAULT_OUTPUT_ENCODING,
               formatter="minimal"):
        """Returns a Unicode representation of this tag and its contents.
 
        :param eventual_encoding: The tag is destined to be
           encoded into this encoding. This method is _not_
           responsible for performing that encoding. This information
           is passed in so that it can be substituted in if the
           document contains a <META> tag that mentions the document's
           encoding.
        """
 
        # First off, turn a string formatter into a Formatter object. This
        # will stop the lookup from happening over and over again.
        if not isinstance(formatter, Formatter) and not callable(formatter):
            formatter = self._formatter_for_name(formatter)
        attrs = []
        if self.attrs:
            for key, val in sorted(self.attrs.items()):
                if val is None:
                    decoded = key
                else:
                    if isinstance(val, list) or isinstance(val, tuple):
                        val = ' '.join(val)
                    elif not isinstance(val, str):
                        val = str(val)
                    elif (
                        isinstance(val, AttributeValueWithCharsetSubstitution)
                        and eventual_encoding is not None):
                        val = val.encode(eventual_encoding)
 
                    text = self.format_string(val, formatter)
                    decoded = (
                        str(key) + '='
                        + EntitySubstitution.quoted_attribute_value(text))
                attrs.append(decoded)
        close = ''
        closeTag = ''
 
        prefix = ''
        if self.prefix:
            prefix = self.prefix + ":"
 
        if self.is_empty_element:
            close = ''
            if isinstance(formatter, Formatter):
                close = formatter.void_element_close_prefix or close
        else:
            closeTag = '</%s%s>' % (prefix, self.name)
 
        pretty_print = self._should_pretty_print(indent_level)
        space = ''
        indent_space = ''
        if indent_level is not None:
            indent_space = (' ' * (indent_level - 1))
        if pretty_print:
            space = indent_space
            indent_contents = indent_level + 1
        else:
            indent_contents = None
        contents = self.decode_contents(
            indent_contents, eventual_encoding, formatter)
 
        if self.hidden:
            # This is the 'document root' object.
            s = contents
        else:
            s = []
            attribute_string = ''
            if attrs:
                attribute_string = ' ' + ' '.join(attrs)
            if indent_level is not None:
                # Even if this particular tag is not pretty-printed,
                # we should indent up to the start of the tag.
                s.append(indent_space)
            s.append('<%s%s%s%s>' % (
                    prefix, self.name, attribute_string, close))
            if pretty_print:
                s.append("\n")
            s.append(contents)
            if pretty_print and contents and contents[-1] != "\n":
                s.append("\n")
            if pretty_print and closeTag:
                s.append(space)
            s.append(closeTag)
            if indent_level is not None and closeTag and self.next_sibling:
                # Even if this particular tag is not pretty-printed,
                # we're now done with the tag, and we should add a
                # newline if appropriate.
                s.append("\n")
            s = ''.join(s)
        return s
 
    def prettify(self, encoding=None, formatter="minimal"):
        if encoding is None:
            return self.decode(True, formatter=formatter)
        else:
            return self.encode(encoding, True, formatter=formatter)
 
    def decode_contents(self, indent_level=None,
                       eventual_encoding=DEFAULT_OUTPUT_ENCODING,
                       formatter="minimal"):
        """Renders the contents of this tag as a Unicode string.
 
        :param indent_level: Each line of the rendering will be
           indented this many spaces.
 
        :param eventual_encoding: The tag is destined to be
           encoded into this encoding. This method is _not_
           responsible for performing that encoding. This information
           is passed in so that it can be substituted in if the
           document contains a <META> tag that mentions the document's
           encoding.
 
        :param formatter: The output formatter responsible for converting
           entities to Unicode characters.
        """
        # First off, turn a string formatter into a Formatter object. This
        # will stop the lookup from happening over and over again.
        if not isinstance(formatter, Formatter) and not callable(formatter):
            formatter = self._formatter_for_name(formatter)
 
        pretty_print = (indent_level is not None)
        s = []
        for c in self:
            text = None
            if isinstance(c, NavigableString):
                text = c.output_ready(formatter)
            elif isinstance(c, Tag):
                s.append(c.decode(indent_level, eventual_encoding,
                                  formatter))
            if text and indent_level and not self.name == 'pre':
                text = text.strip()
            if text:
                if pretty_print and not self.name == 'pre':
                    s.append(" " * (indent_level - 1))
                s.append(text)
                if pretty_print and not self.name == 'pre':
                    s.append("\n")
        return ''.join(s)
 
    def encode_contents(
        self, indent_level=None, encoding=DEFAULT_OUTPUT_ENCODING,
        formatter="minimal"):
        """Renders the contents of this tag as a bytestring.
 
        :param indent_level: Each line of the rendering will be
           indented this many spaces.
 
        :param eventual_encoding: The bytestring will be in this encoding.
 
        :param formatter: The output formatter responsible for converting
           entities to Unicode characters.
        """
 
        contents = self.decode_contents(indent_level, encoding, formatter)
        return contents.encode(encoding)
 
    # Old method for BS3 compatibility
    def renderContents(self, encoding=DEFAULT_OUTPUT_ENCODING,
                       prettyPrint=False, indentLevel=0):
        if not prettyPrint:
            indentLevel = None
        return self.encode_contents(
            indent_level=indentLevel, encoding=encoding)
 
    #Soup methods
 
    def find(self, name=None, attrs={}, recursive=True, text=None,
             **kwargs):
        """Return only the first child of this Tag matching the given
        criteria."""
        r = None
        l = self.find_all(name, attrs, recursive, text, 1, **kwargs)
        if l:
            r = l[0]
        return r
    findChild = find
 
    def find_all(self, name=None, attrs={}, recursive=True, text=None,
                 limit=None, **kwargs):
        """Extracts a list of Tag objects that match the given
        criteria.  You can specify the name of the Tag and any
        attributes you want the Tag to have.
 
        The value of a key-value pair in the 'attrs' map can be a
        string, a list of strings, a regular expression object, or a
        callable that takes a string and returns whether or not the
        string matches for some custom definition of 'matches'. The
        same is true of the tag name."""
 
        generator = self.descendants
        if not recursive:
            generator = self.children
        return self._find_all(name, attrs, text, limit, generator, **kwargs)
    findAll = find_all       # BS3
    findChildren = find_all  # BS2
 
    #Generator methods
    @property
    def children(self):
        # return iter() to make the purpose of the method clear
        return iter(self.contents)  # XXX This seems to be untested.
 
    @property
    def descendants(self):
        if not len(self.contents):
            return
        stopNode = self._last_descendant().next_element
        current = self.contents[0]
        while current is not stopNode:
            yield current
            current = current.next_element
 
    # CSS selector code
 
    _selector_combinators = ['>', '+', '~']
    _select_debug = False
    quoted_colon = re.compile('"[^"]*:[^"]*"')
    def select_one(self, selector):
        """Perform a CSS selection operation on the current element."""
        value = self.select(selector, limit=1)
        if value:
            return value[0]
        return None
 
    def select(self, selector, _candidate_generator=None, limit=None):
        """Perform a CSS selection operation on the current element."""
 
        # Handle grouping selectors if ',' exists, ie: p,a
        if ',' in selector:
            context = []
            selectors = [x.strip() for x in selector.split(",")]
 
            # If a selector is mentioned multiple times we don't want
            # to use it more than once.
            used_selectors = set()
 
            # We also don't want to select the same element more than once,
            # if it's matched by multiple selectors.
            selected_object_ids = set()
            for partial_selector in selectors:
                if partial_selector == '':
                    raise ValueError('Invalid group selection syntax: %s' % selector)
                if partial_selector in used_selectors:
                    continue
                used_selectors.add(partial_selector)
                candidates = self.select(partial_selector, limit=limit)
                for candidate in candidates:
                    # This lets us distinguish between distinct tags that
                    # represent the same markup.
                    object_id = id(candidate)
                    if object_id not in selected_object_ids:
                        context.append(candidate)
                        selected_object_ids.add(object_id)
                if limit and len(context) >= limit:
                    break
            return context
        tokens = shlex.split(selector)
        current_context = [self]
 
        if tokens[-1] in self._selector_combinators:
            raise ValueError(
                'Final combinator "%s" is missing an argument.' % tokens[-1])
 
        if self._select_debug:
            print('Running CSS selector "%s"' % selector)
 
        for index, token in enumerate(tokens):
            new_context = []
            new_context_ids = set([])
 
            if tokens[index-1] in self._selector_combinators:
                # This token was consumed by the previous combinator. Skip it.
                if self._select_debug:
                    print('  Token was consumed by the previous combinator.')
                continue
 
            if self._select_debug:
                print(' Considering token "%s"' % token)
            recursive_candidate_generator = None
            tag_name = None
 
            # Each operation corresponds to a checker function, a rule
            # for determining whether a candidate matches the
            # selector. Candidates are generated by the active
            # iterator.
            checker = None
 
            m = self.attribselect_re.match(token)
            if m is not None:
                # Attribute selector
                tag_name, attribute, operator, value = m.groups()
                checker = self._attribute_checker(operator, attribute, value)
 
            elif '#' in token:
                # ID selector
                tag_name, tag_id = token.split('#', 1)
                def id_matches(tag):
                    return tag.get('id', None) == tag_id
                checker = id_matches
 
            elif '.' in token:
                # Class selector
                tag_name, klass = token.split('.', 1)
                classes = set(klass.split('.'))
                def classes_match(candidate):
                    return classes.issubset(candidate.get('class', []))
                checker = classes_match
 
            elif ':' in token and not self.quoted_colon.search(token):
                # Pseudo-class
                tag_name, pseudo = token.split(':', 1)
                if tag_name == '':
                    raise ValueError(
                        "A pseudo-class must be prefixed with a tag name.")
                pseudo_attributes = re.match(r'([a-zA-Z\d-]+)\(([a-zA-Z\d]+)\)', pseudo)
                found = []
                if pseudo_attributes is None:
                    pseudo_type = pseudo
                    pseudo_value = None
                else:
                    pseudo_type, pseudo_value = pseudo_attributes.groups()
                if pseudo_type == 'nth-of-type':
                    try:
                        pseudo_value = int(pseudo_value)
                    except:
                        raise NotImplementedError(
                            'Only numeric values are currently supported for the nth-of-type pseudo-class.')
                    if pseudo_value < 1:
                        raise ValueError(
                            'nth-of-type pseudo-class value must be at least 1.')
                    class Counter(object):
                        def __init__(self, destination):
                            self.count = 0
                            self.destination = destination
 
                        def nth_child_of_type(self, tag):
                            self.count += 1
                            if self.count == self.destination:
                                return True
                            else:
                                return False
                    checker = Counter(pseudo_value).nth_child_of_type
                else:
                    raise NotImplementedError(
                        'Only the following pseudo-classes are implemented: nth-of-type.')
 
            elif token == '*':
                # Star selector -- matches everything
                pass
            elif token == '>':
                # Run the next token as a CSS selector against the
                # direct children of each tag in the current context.
                recursive_candidate_generator = lambda tag: tag.children
            elif token == '~':
                # Run the next token as a CSS selector against the
                # siblings of each tag in the current context.
                recursive_candidate_generator = lambda tag: tag.next_siblings
            elif token == '+':
                # For each tag in the current context, run the next
                # token as a CSS selector against the tag's next
                # sibling that's a tag.
                def next_tag_sibling(tag):
                    yield tag.find_next_sibling(True)
                recursive_candidate_generator = next_tag_sibling
 
            elif self.tag_name_re.match(token):
                # Just a tag name.
                tag_name = token
            else:
                raise ValueError(
                    'Unsupported or invalid CSS selector: "%s"' % token)
            if recursive_candidate_generator:
                # This happens when the selector looks like  "> foo".
                #
                # The generator calls select() recursively on every
                # member of the current context, passing in a different
                # candidate generator and a different selector.
                #
                # In the case of "> foo", the candidate generator is
                # one that yields a tag's direct children (">"), and
                # the selector is "foo".
                next_token = tokens[index+1]
                def recursive_select(tag):
                    if self._select_debug:
                        print('    Calling select("%s") recursively on %s %s' % (next_token, tag.name, tag.attrs))
                        print('-' * 40)
                    for i in tag.select(next_token, recursive_candidate_generator):
                        if self._select_debug:
                            print('(Recursive select picked up candidate %s %s)' % (i.name, i.attrs))
                        yield i
                    if self._select_debug:
                        print('-' * 40)
                _use_candidate_generator = recursive_select
            elif _candidate_generator is None:
                # By default, a tag's candidates are all of its
                # children. If tag_name is defined, only yield tags
                # with that name.
                if self._select_debug:
                    if tag_name:
                        check = "[any]"
                    else:
                        check = tag_name
                    print('   Default candidate generator, tag name="%s"' % check)
                if self._select_debug:
                    # This is redundant with later code, but it stops
                    # a bunch of bogus tags from cluttering up the
                    # debug log.
                    def default_candidate_generator(tag):
                        for child in tag.descendants:
                            if not isinstance(child, Tag):
                                continue
                            if tag_name and not child.name == tag_name:
                                continue
                            yield child
                    _use_candidate_generator = default_candidate_generator
                else:
                    _use_candidate_generator = lambda tag: tag.descendants
            else:
                _use_candidate_generator = _candidate_generator
 
            count = 0
            for tag in current_context:
                if self._select_debug:
                    print("    Running candidate generator on %s %s" % (
                        tag.name, repr(tag.attrs)))
                for candidate in _use_candidate_generator(tag):
                    if not isinstance(candidate, Tag):
                        continue
                    if tag_name and candidate.name != tag_name:
                        continue
                    if checker is not None:
                        try:
                            result = checker(candidate)
                        except StopIteration:
                            # The checker has decided we should no longer
                            # run the generator.
                            break
                    if checker is None or result:
                        if self._select_debug:
                            print("     SUCCESS %s %s" % (candidate.name, repr(candidate.attrs)))
                        if id(candidate) not in new_context_ids:
                            # If a tag matches a selector more than once,
                            # don't include it in the context more than once.
                            new_context.append(candidate)
                            new_context_ids.add(id(candidate))
                    elif self._select_debug:
                        print("     FAILURE %s %s" % (candidate.name, repr(candidate.attrs)))
 
            current_context = new_context
        if limit and len(current_context) >= limit:
            current_context = current_context[:limit]
 
        if self._select_debug:
            print("Final verdict:")
            for i in current_context:
                print(" %s %s" % (i.name, i.attrs))
        return current_context
 
    # Old names for backwards compatibility
    def childGenerator(self):
        return self.children
 
    def recursiveChildGenerator(self):
        return self.descendants
 
    def has_key(self, key):
        """This was kind of misleading because has_key() (attributes)
        was different from __in__ (contents). has_key() is gone in
        Python 3, anyway."""
        warnings.warn('has_key is deprecated. Use has_attr("%s") instead.' % (
                key))
        return self.has_attr(key)
 
# Next, a couple classes to represent queries and their results.
class SoupStrainer(object):
    """Encapsulates a number of ways of matching a markup element (tag or
    text)."""
 
    def __init__(self, name=None, attrs={}, text=None, **kwargs):
        self.name = self._normalize_search_value(name)
        if not isinstance(attrs, dict):
            # Treat a non-dict value for attrs as a search for the 'class'
            # attribute.
            kwargs['class'] = attrs
            attrs = None
 
        if 'class_' in kwargs:
            # Treat class_="foo" as a search for the 'class'
            # attribute, overriding any non-dict value for attrs.
            kwargs['class'] = kwargs['class_']
            del kwargs['class_']
 
        if kwargs:
            if attrs:
                attrs = attrs.copy()
                attrs.update(kwargs)
            else:
                attrs = kwargs
        normalized_attrs = {}
        for key, value in list(attrs.items()):
            normalized_attrs[key] = self._normalize_search_value(value)
 
        self.attrs = normalized_attrs
        self.text = self._normalize_search_value(text)
 
    def _normalize_search_value(self, value):
        # Leave it alone if it's a Unicode string, a callable, a
        # regular expression, a boolean, or None.
        if (isinstance(value, str) or callable(value) or hasattr(value, 'match')
            or isinstance(value, bool) or value is None):
            return value
 
        # If it's a bytestring, convert it to Unicode, treating it as UTF-8.
        if isinstance(value, bytes):
            return value.decode("utf8")
 
        # If it's listlike, convert it into a list of strings.
        if hasattr(value, '__iter__'):
            new_value = []
            for v in value:
                if (hasattr(v, '__iter__') and not isinstance(v, bytes)
                    and not isinstance(v, str)):
                    # This is almost certainly the user's mistake. In the
                    # interests of avoiding infinite loops, we'll let
                    # it through as-is rather than doing a recursive call.
                    new_value.append(v)
                else:
                    new_value.append(self._normalize_search_value(v))
            return new_value
 
        # Otherwise, convert it into a Unicode string.
        # The unicode(str()) thing is so this will do the same thing on Python 2
        # and Python 3.
        return str(str(value))
 
    def __str__(self):
        if self.text:
            return self.text
        else:
            return "%s|%s" % (self.name, self.attrs)
 
    def search_tag(self, markup_name=None, markup_attrs={}):
        found = None
        markup = None
        if isinstance(markup_name, Tag):
            markup = markup_name
            markup_attrs = markup
        call_function_with_tag_data = (
            isinstance(self.name, Callable)
            and not isinstance(markup_name, Tag))
 
        if ((not self.name)
            or call_function_with_tag_data
            or (markup and self._matches(markup, self.name))
            or (not markup and self._matches(markup_name, self.name))):
            if call_function_with_tag_data:
                match = self.name(markup_name, markup_attrs)
            else:
                match = True
                markup_attr_map = None
                for attr, match_against in list(self.attrs.items()):
                    if not markup_attr_map:
                        if hasattr(markup_attrs, 'get'):
                            markup_attr_map = markup_attrs
                        else:
                            markup_attr_map = {}
                            for k, v in markup_attrs:
                                markup_attr_map[k] = v
                    attr_value = markup_attr_map.get(attr)
                    if not self._matches(attr_value, match_against):
                        match = False
                        break
            if match:
                if markup:
                    found = markup
                else:
                    found = markup_name
        if found and self.text and not self._matches(found.string, self.text):
            found = None
        return found
    searchTag = search_tag
 
    def search(self, markup):
        # print 'looking for %s in %s' % (self, markup)
        found = None
        # If given a list of items, scan it for a text element that
        # matches.
        if hasattr(markup, '__iter__') and not isinstance(markup, (Tag, str)):
            for element in markup:
                if isinstance(element, NavigableString) \
                       and self.search(element):
                    found = element
                    break
        # If it's a Tag, make sure its name or attributes match.
        # Don't bother with Tags if we're searching for text.
        elif isinstance(markup, Tag):
            if not self.text or self.name or self.attrs:
                found = self.search_tag(markup)
        # If it's text, make sure the text matches.
        elif isinstance(markup, NavigableString) or \
                 isinstance(markup, str):
            if not self.name and not self.attrs and self._matches(markup, self.text):
                found = markup
        else:
            raise Exception(
                "I don't know how to match against a %s" % markup.__class__)
        return found
 
    def _matches(self, markup, match_against, already_tried=None):
        # print u"Matching %s against %s" % (markup, match_against)
        result = False
        if isinstance(markup, list) or isinstance(markup, tuple):
            # This should only happen when searching a multi-valued attribute
            # like 'class'.
            for item in markup:
                if self._matches(item, match_against):
                    return True
            # We didn't match any particular value of the multivalue
            # attribute, but maybe we match the attribute value when
            # considered as a string.
            if self._matches(' '.join(markup), match_against):
                return True
            return False
 
        if match_against is True:
            # True matches any non-None value.
            return markup is not None
 
        if isinstance(match_against, Callable):
            return match_against(markup)
 
        # Custom callables take the tag as an argument, but all
        # other ways of matching match the tag name as a string.
        original_markup = markup
        if isinstance(markup, Tag):
            markup = markup.name
 
        # Ensure that `markup` is either a Unicode string, or None.
        markup = self._normalize_search_value(markup)
 
        if markup is None:
            # None matches None, False, an empty string, an empty list, and so on.
            return not match_against
 
        if (hasattr(match_against, '__iter__')
            and not isinstance(match_against, str)):
            # We're asked to match against an iterable of items.
            # The markup must be match at least one item in the
            # iterable. We'll try each one in turn.
            #
            # To avoid infinite recursion we need to keep track of
            # items we've already seen.
            if not already_tried:
                already_tried = set()
            for item in match_against:
                if item.__hash__:
                    key = item
                else:
                    key = id(item)
                if key in already_tried:
                    continue
                else:
                    already_tried.add(key)
                    if self._matches(original_markup, item, already_tried):
                        return True
            else:
                return False
 
        # Beyond this point we might need to run the test twice: once against
        # the tag's name and once against its prefixed name.
        match = False
 
        if not match and isinstance(match_against, str):
            # Exact string match
            match = markup == match_against
 
        if not match and hasattr(match_against, 'search'):
            # Regexp match
            return match_against.search(markup)
 
        if (not match
            and isinstance(original_markup, Tag)
            and original_markup.prefix):
            # Try the whole thing again with the prefixed tag name.
            return self._matches(
                original_markup.prefix + ':' + original_markup.name, match_against
            )
 
        return match
 
class ResultSet(list):
    """A ResultSet is just a list that keeps track of the SoupStrainer
    that created it."""
    def __init__(self, source, result=()):
        super(ResultSet, self).__init__(result)
        self.source = source
 
    def __getattr__(self, key):
        raise AttributeError(
            "ResultSet object has no attribute '%s'. You're probably treating a list of items like a single item. Did you call find_all() when you meant to call find()?" % key
        )