`setattr()` on Python2 `_sre.SRE_Pattern` - python-2.7

Question

I'm basically attempting py2/3 compatibility by trying to add a a fullmatch method to Python2 re compiled patterns.
I've seen https://stackoverflow.com/a/2982/2694385 on how to add an attribute to an existing instance.
I'm creating the method as given in https://stackoverflow.com/a/30212799/2694385.
Example code
import re
import six
regex = re.compile('some pattern') # Better if we keep this same
if six.PY2:
def fullmatch(self_regex, string, flags=0):
return self_regex.match(string, flags=flags)
regex = re.compile(r'(?:' + regex.pattern + r')\Z', flags=regex.flags)
import types
bound = types.MethodType(fullmatch, regex)
# AttributeError here. None of the following three lines work
regex.fullmatch = bound
regex.__setattr__('fullmatch', bound)
setattr(regex, 'fullmatch', bound)

Answer 1

That ain't gonna work - regex objects are created on the C side and they don't represent your regular instances so you cannot modify their signature from within Python. For example, if you try to extend _sre.SRE_Pattern:
import _sre
class CustomPattern(_sre.SRE_Pattern): pass
You'll get an AttributeError complaining that such object doesn't exist in the _sre module. If you try to cheat it with:
import re
tmp_pattern = re.compile("")
sre_pat = type(tmp_pattern)
class CustomPattern(sre_pat): pass
it will give you a TypeError complaining that _sre.SRE_Pattern (which now 'temporarily' exists as it's being created ad-hoc) is not an acceptable base type.
What you can do instead is to create a full wrapper around the re module (or at least add the missing structures to it) and handle the Python version differences on the Python's side, although I think it's just not worth it.
P.S. If you're not using six anywhere else, there no reason for the overhead just to check your Python version - you can use sys.version_info.major < 3 instead.

Answer 2

See nlpia.regexes.Pattern for something similar to what you want -- a Frankenstein mashup of _sre.Pattern with a fullmatch() method. This monkey-patching "inheritance" approach works in Python 2 and 3.
import re
import regex
class Pattern:
""" "Inherits" _sre.SRE_Pattern and adds .fullmatch() method
>>> pattern = Pattern('Aaron[ ]Swartz')
>>> pattern.match('Aaron Swartz')
<_sre.SRE_Match object; span=(0, 12), match='Aaron Swartz'>
>>> pattern.fullmatch('Aaron Swartz!!')
>>> pattern.match('Aaron Swartz!!')
<_sre.SRE_Match object; span=(0, 12), match='Aaron Swartz'>
"""
def __init__(self, pattern):
self._compiled_pattern = re.compile(pattern)
for name in dir(self._compiled_pattern):
if not name in set(('__class__', '__init__', 'fullmatch')):
attr = getattr(self._compiled_pattern, name)
setattr(self, name, attr)
def fullmatch(self, *args, **kwargs):
return regex.fullmatch(self._compiled_pattern.pattern, *args, **kwargs)