Backport Python 3.4's regular expression “fullmatch()” to Python 2

问题

Python 3.4 introduced the new regex method re.fullmatch(pattern, string, flags=0).

Has anyone back-ported this new method to older Python versions?

回答1:

To make sure that the entire string matches, you need to use the \Z end-of-string anchor:

def fullmatch(regex, string, flags=0):
    """Emulate python-3.4 re.fullmatch()."""
    return re.match("(?:" + regex + r")\Z", string, flags=flags)

The \A anchor is not necessary since re.match() already anchors the match to the start of the string.

回答2:

Here it is my backporting, which has at least one problem (thanks tim-pietzcker) but does not require recompiling regexes:

import re

def fullmatch(regex, string, flags=0):
    """Emulate python-3.4 re.fullmatch()."""
    m = re.match(regex, string, flags=flags)
    if m and m.span()[1] == len(string):
        return m

And here are some test-cases proving the above emulation-function.

def compare_expansion(regex, s, template):
    m1 = re.fullmatch(regex, s)
    s1 = m1.expand(template) if m1 else '<NO-MATCH>'
    m2 = fullmatch(regex, s)
    s2 = m2.expand(template) if m2 else '<NO-MATCH>'
    if s1 != s2:
        raise AssertionError("\n  PY-3: '%s' \n  PY-2: '%s' " % (s1, s2))

compare_expansion('.*', 'foo', r'A')
compare_expansion('(.*)', 'foo', r'A_\1')
compare_expansion('(.*)', 'foo', r'A_\g<0>')

compare_expansion('a.*', 'afoo&', r'A')
compare_expansion('a(\w*)', 'afoo&', r'A_\1')
compare_expansion('a(\w*)', 'afoo&', r'A_\g<0>')

## But this fails!
compare_expansion(".*?", "Hello", '\g<0>')
AssertionError: 
  PY-3: 'A_Hello' 
  PY-2: '<NO-MATCH>'

来源：https://stackoverflow.com/questions/30212413/backport-python-3-4s-regular-expression-fullmatch-to-python-2

标签

python

regex

python-3.x

python-2.x

backport