[Python-Dev] Possible optimization for LOAD_FAST ?

Steven D'Aprano steve at pearwood.info
Tue Jan 4 22:50:44 CET 2011

Guido van Rossum wrote:
> On Tue, Jan 4, 2011 at 2:49 AM, Michael Foord <fuzzyman at voidspace.org.uk> 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.


More information about the Python-Dev mailing list