Guido van Rossum wrote:
On Tue, Jan 4, 2011 at 2:49 AM, Michael Foord firstname.lastname@example.org wrote:
I think someone else pointed this out, but replacing builtins externally to a module is actually common for testing. In particular replacing the open function, but also other builtins, is often done temporarily to replace it with a mock. It seems like this optimisation would break those tests.
Hm, I already suggested to make an exception for open, (and one should be added for __import__) but if this is done for other builtins that is indeed a problem. Can you point to example code doing this?
I've been known to monkey-patch builtins in the interactive interpreter and in test code. One example that comes to mind is that I had some over-complicated recursive while loop (!), and I wanted to work out the Big Oh behaviour so I knew exactly how horrible it was. Working it out from first principles was too hard, so I cheated: I knew each iteration called len() exactly once, so I monkey-patched len() to count how many times it was called. Problem solved.
I also have a statistics package that has its own version of sum, and I rely on calls to sum() from within the package picking up my version rather than the builtin one.