Why is __doc__ imported from the builtin sre module
when a regular expression is substituted replacing a group?


$ python
Python 2.4.1 (#2, Mar 30 2005, 21:51:10)
[GCC 3.3.5 (Debian 1:3.3.5-8ubuntu2)] on linux2
Type "help", "copyright", "credits" or "license" for
more information.

>>> def import_hook(name, globals={}, locals={},
fromlist=[]):
...     print name, fromlist
...     return original_import(name, globals, locals,
fromlist)
...
>>> import __builtin__
>>> original_import = __builtin__.__import__
>>> __builtin__.__import__ = import_hook

>>> import re
re None
sre ('*',)
sys None
sre_compile None
_sre None
sys None
sre_constants ('*',)
sre_parse None
sys None
sre_constants ('*',)
sre_parse None
copy_reg None
sre ('__all__',)

>>> re1 = re.compile('foo...bar')
sre_parse None

>>> re1.sub('x', 'y')
'y'
>>> re1.sub('x', 'fooXXXbar')
'x'

>>> re2 = re.compile('foo(...)bar')
sre_parse None
>>> re2.sub('x', 'y')
'y'
>>> re2.sub('\\1', 'fooXXXbar')
sre ['__doc__']
'XXX'

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user_id=492001

This is significant for programs that use an expensive
import hook, and also use this kind of regex.

I'm working around this by making my import hook return
early for imports from sre.

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user_id=174455

Below is the full source of re.py. Does your problem go away
when you use sre directly instead? 

"""Minimal "re" compatibility wrapper.  See "sre" for
documentation."""

engine = "sre" # Some apps might use this undocumented variable

from sre import *
from sre import __all__

pattern.sub() imports the SRE Python module (to call its subx()) with
PyImport_Import -- that C functions uses a dummy list ['__doc__'] to get
the correct module for dotted import paths.

The import of an additional module is gone now that re is really called re.