Python 进阶 之 traceback模块

Traceback模块官方英文描述：

 Help on module traceback:

 NAME
     traceback - Extract, format and print information about Python stack traces.

 FILE
     /usr/lib64/python2.7/traceback.py

 FUNCTIONS
     extract_stack(f=None, limit=None)
         Extract the raw traceback from the current stack frame.

         The return value has the same format as for extract_tb().  The
         optional 'f' and 'limit' arguments have the same meaning as for
         print_stack().  Each item in the list is a quadruple (filename,
         line number, function name, text), and the entries are in order
         from oldest to newest stack frame.

     extract_tb(tb, limit=None)
         Return list of up to limit pre-processed entries from traceback.

         This is useful for alternate formatting of stack traces.  If
         'limit' is omitted or None, all entries are extracted.  A
         pre-processed stack trace entry is a quadruple (filename, line
         number, function name, text) representing the information that is
         usually printed for a stack trace.  The text is a string with
         leading and trailing whitespace stripped; if the source is not
         available it is None.

     format_exc(limit=None)
         Like print_exc() but return a string.

     format_exception(etype, value, tb, limit=None)
         Format a stack trace and the exception information.

         The arguments have the same meaning as the corresponding arguments
         to print_exception().  The return value is a list of strings, each
         ending in a newline and some containing internal newlines.  When
         these lines are concatenated and printed, exactly the same text is
         printed as does print_exception().

     format_exception_only(etype, value)
         Format the exception part of a traceback.

         The arguments are the exception type and value such as given by
         sys.last_type and sys.last_value. The return value is a list of
         strings, each ending in a newline.

         Normally, the list contains a single string; however, for
         SyntaxError exceptions, it contains several lines that (when
         printed) display detailed information about where the syntax
         error occurred.

         The message indicating which exception occurred is always the last
         string in the list.

     format_list(extracted_list)
         Format a list of traceback entry tuples for printing.

         Given a list of tuples as returned by extract_tb() or
         extract_stack(), return a list of strings ready for printing.
         Each string in the resulting list corresponds to the item with the
         same index in the argument list.  Each string ends in a newline;
         the strings may contain internal newlines as well, for those items
         whose source text line is not None.

     format_stack(f=None, limit=None)
         Shorthand for 'format_list(extract_stack(f, limit))'.

     format_tb(tb, limit=None)
         A shorthand for 'format_list(extract_stack(f, limit)).

     print_exc(limit=None, file=None)
         Shorthand for 'print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)'.
         (In fact, it uses sys.exc_info() to retrieve the same information
         in a thread-safe way.)

     print_exception(etype, value, tb, limit=None, file=None)
         Print exception up to 'limit' stack trace entries from 'tb' to 'file'.

         This differs from print_tb() in the following ways: (1) if
         traceback is not None, it prints a header "Traceback (most recent
         call last):"; (2) it prints the exception type and value after the
         stack trace; (3) if type is SyntaxError and value has the
         appropriate format, it prints the line where the syntax error
         occurred with a caret on the next line indicating the approximate
         position of the error.

     print_last(limit=None, file=None)
         This is a shorthand for 'print_exception(sys.last_type,
         sys.last_value, sys.last_traceback, limit, file)'.

     print_stack(f=None, limit=None, file=None)
         Print a stack trace from its invocation point.

         The optional 'f' argument can be used to specify an alternate
         stack frame at which to start. The optional 'limit' and 'file'
         arguments have the same meaning as for print_exception().

     print_tb(tb, limit=None, file=None)
         Print up to 'limit' stack trace entries from the traceback 'tb'.

         If 'limit' is omitted or None, all entries are printed.  If 'file'
         is omitted or None, the output goes to sys.stderr; otherwise
         'file' should be an open file or file-like object with a write()
         method.

     tb_lineno(tb)
         Calculate correct line number of traceback given in tb.

         Obsolete in 2.3.

 DATA
     __all__ = ['extract_stack', 'extract_tb', 'format_exception', 'format_...

 (END)

traceback.py源码（Python2.7.5）：

 """Extract, format and print information about Python stack traces."""

 import linecache
 import sys
 import types

 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
            'format_exception_only', 'format_list', 'format_stack',
            'format_tb', 'print_exc', 'format_exc', 'print_exception',
            'print_last', 'print_stack', 'print_tb', 'tb_lineno']

 def _print(file, str='', terminator='\n'):
     file.write(str+terminator)

 def print_list(extracted_list, file=None):
     """Print the list of tuples as returned by extract_tb() or
     extract_stack() as a formatted stack trace to the given file."""
     if file is None:
         file = sys.stderr
     for filename, lineno, name, line in extracted_list:
         _print(file,
                '  File "%s", line %d, in %s' % (filename,lineno,name))
         if line:
             _print(file, '    %s' % line.strip())

 def format_list(extracted_list):
     """Format a list of traceback entry tuples for printing.

     Given a list of tuples as returned by extract_tb() or
     extract_stack(), return a list of strings ready for printing.
     Each string in the resulting list corresponds to the item with the
     same index in the argument list.  Each string ends in a newline;
     the strings may contain internal newlines as well, for those items
     whose source text line is not None.
     """
     list = []
     for filename, lineno, name, line in extracted_list:
         item = '  File "%s", line %d, in %s\n' % (filename,lineno,name)
         if line:
             item = item + '    %s\n' % line.strip()
         list.append(item)
     return list

 def print_tb(tb, limit=None, file=None):
     """Print up to 'limit' stack trace entries from the traceback 'tb'.

     If 'limit' is omitted or None, all entries are printed.  If 'file'
     is omitted or None, the output goes to sys.stderr; otherwise
     'file' should be an open file or file-like object with a write()
     method.
     """
     if file is None:
         file = sys.stderr
     if limit is None:
         if hasattr(sys, 'tracebacklimit'):
             limit = sys.tracebacklimit
     n = 0
     while tb is not None and (limit is None or n < limit):
         f = tb.tb_frame
         lineno = tb.tb_lineno
         co = f.f_code
         filename = co.co_filename
         name = co.co_name
         _print(file,
                '  File "%s", line %d, in %s' % (filename, lineno, name))
         linecache.checkcache(filename)
         line = linecache.getline(filename, lineno, f.f_globals)
         if line: _print(file, '    ' + line.strip())
         tb = tb.tb_next
         n = n+1

 def format_tb(tb, limit = None):
     """A shorthand for 'format_list(extract_stack(f, limit))."""
     return format_list(extract_tb(tb, limit))

 def extract_tb(tb, limit = None):
     """Return list of up to limit pre-processed entries from traceback.

     This is useful for alternate formatting of stack traces.  If
     'limit' is omitted or None, all entries are extracted.  A
     pre-processed stack trace entry is a quadruple (filename, line
     number, function name, text) representing the information that is
     usually printed for a stack trace.  The text is a string with
     leading and trailing whitespace stripped; if the source is not
     available it is None.
     """
     if limit is None:
         if hasattr(sys, 'tracebacklimit'):
             limit = sys.tracebacklimit
     list = []
     n = 0
     while tb is not None and (limit is None or n < limit):
         f = tb.tb_frame
         lineno = tb.tb_lineno
         co = f.f_code
         filename = co.co_filename
         name = co.co_name
         linecache.checkcache(filename)
         line = linecache.getline(filename, lineno, f.f_globals)
         if line: line = line.strip()
         else: line = None
         list.append((filename, lineno, name, line))
         tb = tb.tb_next
         n = n+1
     return list

 def print_exception(etype, value, tb, limit=None, file=None):
     """Print exception up to 'limit' stack trace entries from 'tb' to 'file'.

     This differs from print_tb() in the following ways: (1) if
     traceback is not None, it prints a header "Traceback (most recent
     call last):"; (2) it prints the exception type and value after the
     stack trace; (3) if type is SyntaxError and value has the
     appropriate format, it prints the line where the syntax error
     occurred with a caret on the next line indicating the approximate
     position of the error.
     """
     if file is None:
         file = sys.stderr
     if tb:
         _print(file, 'Traceback (most recent call last):')
         print_tb(tb, limit, file)
     lines = format_exception_only(etype, value)
     for line in lines:
         _print(file, line, '')

 def format_exception(etype, value, tb, limit = None):
     """Format a stack trace and the exception information.

     The arguments have the same meaning as the corresponding arguments
     to print_exception().  The return value is a list of strings, each
     ending in a newline and some containing internal newlines.  When
     these lines are concatenated and printed, exactly the same text is
     printed as does print_exception().
     """
     if tb:
         list = ['Traceback (most recent call last):\n']
         list = list + format_tb(tb, limit)
     else:
         list = []
     list = list + format_exception_only(etype, value)
     return list

 def format_exception_only(etype, value):
     """Format the exception part of a traceback.

     The arguments are the exception type and value such as given by
     sys.last_type and sys.last_value. The return value is a list of
     strings, each ending in a newline.

     Normally, the list contains a single string; however, for
     SyntaxError exceptions, it contains several lines that (when
     printed) display detailed information about where the syntax
     error occurred.

     The message indicating which exception occurred is always the last
     string in the list.

     """

     # An instance should not have a meaningful value parameter, but
     # sometimes does, particularly for string exceptions, such as
     # >>> raise string1, string2  # deprecated
     #
     # Clear these out first because issubtype(string1, SyntaxError)
     # would raise another exception and mask the original problem.
     if (isinstance(etype, BaseException) or
         isinstance(etype, types.InstanceType) or
         etype is None or type(etype) is str):
         return [_format_final_exc_line(etype, value)]

     stype = etype.__name__

     if not issubclass(etype, SyntaxError):
         return [_format_final_exc_line(stype, value)]

     # It was a syntax error; show exactly where the problem was found.
     lines = []
     try:
         msg, (filename, lineno, offset, badline) = value.args
     except Exception:
         pass
     else:
         filename = filename or "<string>"
         lines.append('  File "%s", line %d\n' % (filename, lineno))
         if badline is not None:
             lines.append('    %s\n' % badline.strip())
             if offset is not None:
                 caretspace = badline.rstrip('\n')[:offset].lstrip()
                 # non-space whitespace (likes tabs) must be kept for alignment
                 caretspace = ((c.isspace() and c or ' ') for c in caretspace)
                 # only three spaces to account for offset1 == pos 0
                 lines.append('   %s^\n' % ''.join(caretspace))
         value = msg

     lines.append(_format_final_exc_line(stype, value))
     return lines

 def _format_final_exc_line(etype, value):
     """Return a list of a single line -- normal case for format_exception_only"""
     valuestr = _some_str(value)
     if value is None or not valuestr:
         line = "%s\n" % etype
     else:
         line = "%s: %s\n" % (etype, valuestr)
     return line

 def _some_str(value):
     try:
         return str(value)
     except Exception:
         pass
     try:
         value = unicode(value)
         return value.encode("ascii", "backslashreplace")
     except Exception:
         pass
     return '<unprintable %s object>' % type(value).__name__

 def print_exc(limit=None, file=None):
     """Shorthand for 'print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)'.
     (In fact, it uses sys.exc_info() to retrieve the same information
     in a thread-safe way.)"""
     if file is None:
         file = sys.stderr
     try:
         etype, value, tb = sys.exc_info()
         print_exception(etype, value, tb, limit, file)
     finally:
         etype = value = tb = None

 def format_exc(limit=None):
     """Like print_exc() but return a string."""
     try:
         etype, value, tb = sys.exc_info()
         return ''.join(format_exception(etype, value, tb, limit))
     finally:
         etype = value = tb = None

 def print_last(limit=None, file=None):
     """This is a shorthand for 'print_exception(sys.last_type,
     sys.last_value, sys.last_traceback, limit, file)'."""
     if not hasattr(sys, "last_type"):
         raise ValueError("no last exception")
     if file is None:
         file = sys.stderr
     print_exception(sys.last_type, sys.last_value, sys.last_traceback,
                     limit, file)

 def print_stack(f=None, limit=None, file=None):
     """Print a stack trace from its invocation point.

     The optional 'f' argument can be used to specify an alternate
     stack frame at which to start. The optional 'limit' and 'file'
     arguments have the same meaning as for print_exception().
     """
     if f is None:
         try:
             raise ZeroDivisionError
         except ZeroDivisionError:
             f = sys.exc_info()[2].tb_frame.f_back
     print_list(extract_stack(f, limit), file)

 def format_stack(f=None, limit=None):
     """Shorthand for 'format_list(extract_stack(f, limit))'."""
     if f is None:
         try:
             raise ZeroDivisionError
         except ZeroDivisionError:
             f = sys.exc_info()[2].tb_frame.f_back
     return format_list(extract_stack(f, limit))

 def extract_stack(f=None, limit = None):
     """Extract the raw traceback from the current stack frame.

     The return value has the same format as for extract_tb().  The
     optional 'f' and 'limit' arguments have the same meaning as for
     print_stack().  Each item in the list is a quadruple (filename,
     line number, function name, text), and the entries are in order
     from oldest to newest stack frame.
     """
     if f is None:
         try:
             raise ZeroDivisionError
         except ZeroDivisionError:
             f = sys.exc_info()[2].tb_frame.f_back
     if limit is None:
         if hasattr(sys, 'tracebacklimit'):
             limit = sys.tracebacklimit
     list = []
     n = 0
     while f is not None and (limit is None or n < limit):
         lineno = f.f_lineno
         co = f.f_code
         filename = co.co_filename
         name = co.co_name
         linecache.checkcache(filename)
         line = linecache.getline(filename, lineno, f.f_globals)
         if line: line = line.strip()
         else: line = None
         list.append((filename, lineno, name, line))
         f = f.f_back
         n = n+1
     list.reverse()
     return list

 def tb_lineno(tb):
     """Calculate correct line number of traceback given in tb.

     Obsolete in 2.3.
     """
     return tb.tb_lineno