PYTHON3 RE正则表达：

 The special characters are:
     "."      Matches any character except a newline.
     "^"      Matches the start of the string.
     "$"      Matches the end of the string or just before the newline at
              the end of the string.
     "*"      Matches 0 or more (greedy) repetitions of the preceding RE.
              Greedy means that it will match as many repetitions as possible.
     "+"      Matches 1 or more (greedy) repetitions of the preceding RE.
     "?"      Matches 0 or 1 (greedy) of the preceding RE.
     *?,+?,?? Non-greedy versions of the previous three special characters.
     {m,n}    Matches from m to n repetitions of the preceding RE.
     {m,n}?   Non-greedy version of the above.
     "\\"     Either escapes special characters or signals a special sequence.
     []       Indicates a set of characters.
              A "^" as the first character indicates a complementing set.
     "|"      A|B, creates an RE that will match either A or B.
     (...)    Matches the RE inside the parentheses.
              The contents can be retrieved or matched later in the string.
     (?aiLmsux) Set the A, I, L, M, S, U, or X flag for the RE (see below).
     (?:...)  Non-grouping version of regular parentheses.
     (?P<name>...) The substring matched by the group is accessible by name.
     (?P=name)     Matches the text matched earlier by the group named name.
     (?#...)  A comment; ignored.
     (?=...)  Matches if ... matches next, but doesn't consume the string.
     (?!...)  Matches if ... doesn't match next.
     (?<=...) Matches if preceded by ... (must be fixed length).
     (?<!...) Matches if not preceded by ... (must be fixed length).
     (?(id/name)yes|no) Matches yes pattern if the group with id/name matched,
                        the (optional) no pattern otherwise.

 The special sequences consist of "\\" and a character from the list
 below.  If the ordinary character is not on the list, then the
 resulting RE will match the second character.
     \number  Matches the contents of the group of the same number.
     \A       Matches only at the start of the string.
     \Z       Matches only at the end of the string.
     \b       Matches the empty string, but only at the start or end of a word.
     \B       Matches the empty string, but not at the start or end of a word.
     \d       Matches any decimal digit; equivalent to the set [0-9] in
              bytes patterns or string patterns with the ASCII flag.
              In string patterns without the ASCII flag, it will match the whole
              range of Unicode digits.
     \D       Matches any non-digit character; equivalent to [^\d].
     \s       Matches any whitespace character; equivalent to [ \t\n\r\f\v] in
              bytes patterns or string patterns with the ASCII flag.
              In string patterns without the ASCII flag, it will match the whole
              range of Unicode whitespace characters.
     \S       Matches any non-whitespace character; equivalent to [^\s].
     \w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_]
              in bytes patterns or string patterns with the ASCII flag.
              In string patterns without the ASCII flag, it will match the
              range of Unicode alphanumeric characters (letters plus digits
              plus underscore).
              With LOCALE, it will match the set [0-9_] plus characters defined
              as letters for the current locale.
     \W       Matches the complement of \w.
     \\       Matches a literal backslash.

 This module exports the following functions:
     match     Match a regular expression pattern to the beginning of a string.
     fullmatch Match a regular expression pattern to all of a string.
     search    Search a string for the presence of a pattern.
     sub       Substitute occurrences of a pattern found in a string.
     subn      Same as sub, but also return the number of substitutions made.
     split     Split a string by the occurrences of a pattern.
     findall   Find all occurrences of a pattern in a string.
     finditer  Return an iterator yielding a match object for each match.
     compile   Compile a pattern into a RegexObject.
     purge     Clear the regular expression cache.
     escape    Backslash all non-alphanumerics in a string.

 Some of the functions in this module takes flags as optional parameters:
     A  ASCII       For string patterns, make \w, \W, \b, \B, \d, \D
                    match the corresponding ASCII character categories
                    (rather than the whole Unicode categories, which is the
                    default).
                    For bytes patterns, this flag is the only available
                    behaviour and needn't be specified.
     I  IGNORECASE  Perform case-insensitive matching.
     L  LOCALE      Make \w, \W, \b, \B, dependent on the current locale.
     M  MULTILINE   "^" matches the beginning of lines (after a newline)
                    as well as the string.
                    "$" matches the end of lines (before a newline) as well
                    as the end of the string.
     S  DOTALL      "." matches any character at all, including the newline.
     X  VERBOSE     Ignore whitespace and comments for nicer looking RE's.
     U  UNICODE     For compatibility only. Ignored for string patterns (it
                    is the default), and forbidden for bytes patterns.

 # --------------------------------------------------------------------
 # public interface

 def match(pattern, string, flags=0):
     """Try to apply the pattern at the start of the string, returning
     a match object, or None if no match was found."""
     return _compile(pattern, flags).match(string)

 def fullmatch(pattern, string, flags=0):
     """Try to apply the pattern to all of the string, returning
     a match object, or None if no match was found."""
     return _compile(pattern, flags).fullmatch(string)

 def search(pattern, string, flags=0):
     """Scan through string looking for a match to the pattern, returning
     a match object, or None if no match was found."""
     return _compile(pattern, flags).search(string)

 def sub(pattern, repl, string, count=0, flags=0):
     """Return the string obtained by replacing the leftmost
     non-overlapping occurrences of the pattern in string by the
     replacement repl.  repl can be either a string or a callable;
     if a string, backslash escapes in it are processed.  If it is
     a callable, it's passed the match object and must return
     a replacement string to be used."""
     return _compile(pattern, flags).sub(repl, string, count)

 def subn(pattern, repl, string, count=0, flags=0):
     """Return a 2-tuple containing (new_string, number).
     new_string is the string obtained by replacing the leftmost
     non-overlapping occurrences of the pattern in the source
     string by the replacement repl.  number is the number of
     substitutions that were made. repl can be either a string or a
     callable; if a string, backslash escapes in it are processed.
     If it is a callable, it's passed the match object and must
     return a replacement string to be used."""
     return _compile(pattern, flags).subn(repl, string, count)

 def split(pattern, string, maxsplit=0, flags=0):
     """Split the source string by the occurrences of the pattern,
     returning a list containing the resulting substrings.  If
     capturing parentheses are used in pattern, then the text of all
     groups in the pattern are also returned as part of the resulting
     list.  If maxsplit is nonzero, at most maxsplit splits occur,
     and the remainder of the string is returned as the final element
     of the list."""
     return _compile(pattern, flags).split(string, maxsplit)

 def findall(pattern, string, flags=0):
     """Return a list of all non-overlapping matches in the string.

     If one or more capturing groups are present in the pattern, return
     a list of groups; this will be a list of tuples if the pattern
     has more than one group.

     Empty matches are included in the result."""
     return _compile(pattern, flags).findall(string)

 def finditer(pattern, string, flags=0):
     """Return an iterator over all non-overlapping matches in the
     string.  For each match, the iterator returns a match object.

     Empty matches are included in the result."""
     return _compile(pattern, flags).finditer(string)

 def compile(pattern, flags=0):
     "Compile a regular expression pattern, returning a pattern object."
     return _compile(pattern, flags)

 def purge():
     "Clear the regular expression caches"
     _cache.clear()
     _cache_repl.clear()

 def template(pattern, flags=0):
     "Compile a template pattern, returning a pattern object"
     return _compile(pattern, flags|T)

re.py