4.3.2 Module Contents

The module defines these functions, and an exception:

match (pattern, string): Return how many characters at the beginning of string match the regular expression pattern. Return -1 if the string does not match the pattern (this is different from a zero-length match!).

search (pattern, string): Return the first position in string that matches the regular expression pattern. Return -1 if no position in the string matches the pattern (this is different from a zero-length match anywhere!).

compile (pattern[, translate])

Compile a regular expression pattern into a regular expression object, which can be used for matching using its match() and search() methods, described below. The optional argument translate, if present, must be a 256-character string indicating how characters (both of the pattern and of the strings to be matched) are translated before comparing them; the i-th element of the string gives the translation for the character with ASCII code i. This can be used to implement case-insensitive matching; see the casefold data item below.

The sequence

prog = regex.compile(pat)
result = prog.match(str)

is equivalent to

result = regex.match(pat, str)

but the version using compile() is more efficient when multiple regular expressions are used concurrently in a single program. (The compiled version of the last pattern passed to regex.match() or regex.search() is cached, so programs that use only a single regular expression at a time needn't worry about compiling regular expressions.)

set_syntax (flags): Set the syntax to be used by future calls to compile(), match() and search(). (Already compiled expression objects are not affected.) The argument is an integer which is the OR of several flag bits. The return value is the previous value of the syntax flags. Names for the flags are defined in the standard module regex_syntax; read the file regex_syntax.py for more information.

get_syntax (): Returns the current value of the syntax flags as an integer.

symcomp (pattern[, translate]): This is like compile(), but supports symbolic group names: if a parenthesis-enclosed group begins with a group name in angular brackets, e.g. '\(<id>[a-z][a-z0-9]*\)', the group can be referenced by its name in arguments to the group() method of the resulting compiled regular expression object, like this: p.group('id'). Group names may contain alphanumeric characters and '_' only.

error: Exception raised when a string passed to one of the functions here is not a valid regular expression (e.g., unmatched parentheses) or when some other error occurs during compilation or matching. (It is never an error if a string contains no match for a pattern.)

casefold: A string suitable to pass as the translate argument to compile() to map all upper case characters to their lowercase equivalents.

Compiled regular expression objects support these methods:

match (string[, pos]): Return how many characters at the beginning of string match the compiled regular expression. Return -1 if the string does not match the pattern (this is different from a zero-length match!).
The optional second parameter, pos, gives an index in the string where the search is to start; it defaults to 0. This is not completely equivalent to slicing the string; the '' pattern character matches at the real beginning of the string and at positions just after a newline, not necessarily at the index where the search is to start.

search (string[, pos]): Return the first position in string that matches the regular expression pattern. Return -1 if no position in the string matches the pattern (this is different from a zero-length match anywhere!).
The optional second parameter has the same meaning as for the match() method.

group (index, index, ...): This method is only valid when the last call to the match() or search() method found a match. It returns one or more groups of the match. If there is a single index argument, the result is a single string; if there are multiple arguments, the result is a tuple with one item per argument. If the index is zero, the corresponding return value is the entire matching string; if it is in the inclusive range [1..99], it is the string matching the the corresponding parenthesized group (using the default syntax, groups are parenthesized using \( and \)). If no such group exists, the corresponding result is None.
If the regular expression was compiled by symcomp() instead of compile(), the index arguments may also be strings identifying groups by their group name.

Compiled regular expressions support these data attributes:

regs: When the last call to the match() or search() method found a match, this is a tuple of pairs of indexes corresponding to the beginning and end of all parenthesized groups in the pattern. Indices are relative to the string argument passed to match() or search(). The 0-th tuple gives the beginning and end or the whole pattern. When the last match or search failed, this is None.

last: When the last call to the match() or search() method found a match, this is the string argument passed to that method. When the last match or search failed, this is None.

translate: This is the value of the translate argument to regex.compile() that created this regular expression object. If the translate argument was omitted in the regex.compile() call, this is None.

givenpat: The regular expression pattern as passed to compile() or symcomp().

realpat: The regular expression after stripping the group names for regular expressions compiled with symcomp(). Same as givenpat otherwise.

groupindex: A dictionary giving the mapping from symbolic group names to numerical group indexes for regular expressions compiled with symcomp(). None otherwise.

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