The attached patch fixes the OP's use case on the Python side by re-ordering the tests, such that "always" prevents the short-circuit from firing::

 $ ./python 
 Python 2.6.5+ (release26-maint, Apr 29 2010, 21:24:12) 
 [GCC 4.3.3] on linux2
 Type "help", "copyright", "credits" or "license" for more information.
 >>> import warnings as o_warnings
 >>> import sys
 >>> sys.modules['_warnings'] = 0
 >>> del sys.modules['warnings']
 >>> import warnings as py_warnings
 >>> def f():
 ...     py_warnings.warn('foo')
 ... 
 >>> f()
 __main__:2: UserWarning: foo
 >>> f()
 >>> py_warnings.simplefilter('always')
 >>> f()
 __main__:2: UserWarning: foo
 >>> f()
 __main__:2: UserWarning: foo