[Python-Dev] Possible optimization for LOAD_FAST ?

Guido van Rossum guido at python.org
Tue Jan 4 23:15:16 CET 2011

On Tue, Jan 4, 2011 at 1:50 PM, Steven D'Aprano <steve at pearwood.info> wrote:
> 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.

But why couldn't you edit the source code?

> 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.

As long as you have a definition or import of sum at the top of (or
really anywhere in) the module, that will still work. It's only if you
were to do things like

import builtins
builtins.len = ...

(whether inside your package or elsewhere) that things would stop
working with the proposed optimization.

--Guido van Rossum (python.org/~guido)

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