On Fri, Mar 11, 2011 at 6:49 PM, Greg Ewing <greg.ew...@canterbury.ac.nz> wrote: > Thomas Wouters wrote: > >> 2. Make CFunctions turn into methods in CPython (after a period of >> warning about the impending change, obviously.) The actual *usecase* for >> this is hard to envision > > While not necessary for the case being discussed here, this would > be a big help for Pyrex and Cython, where currently some awkward > things have to be done to get a Python class with methods implemented > in C.
I appreciate the use case, but I believe the right solution there is to create a custom decorator implementing the desired descriptor behavior. There simply are too many places where existing code depends on a built-in function placed in a class *not* turning into a method. Also, there is a slippery-slope argument here: if we were to add such a descriptor to CFunctions, why not to other callables? I think we need to stick to the rule where only Python functions have a method-making descriptor. Off-line, I discussed the patch with Thomas and we ended up agreeing that the warning should only be issued for CFunctions used as class variables. In summary, I don't think the problem is with the difference between CFunctions and pure-Python functions. That difference is well-defined and shouldn't go away. The problem is that it is fairly common that something that is a CFunction in CPython is replaced by a pure-Python function, either in another Python VM, or in a different environment (think heapq.py vs. _heapq.c), or when some unittest uses dependency injection (i.e. temporarily replaces a built-in with a wrapper written in Python). Such substitutions are generally transparent, but not when the function is used as a class attribute. We should do all these things to address this: - on the "consuming" side, wrap such class variables in staticmethod() calls - on the "producing" side (e.g. in PyPy) wrap pure-Python functions that are substitutes for CPython builtins in a custom descriptor that prevents method-making - in CPython, warn whenever a built-in function is used as a class variable -- --Guido van Rossum (python.org/~guido) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
