Guido van Rossum wrote:
On Tue, Jan 4, 2011 at 1:50 PM, Steven D'Aprano email@example.com 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?
Because there was no source code -- I was experimenting in the interactive interpreter. I could have just re-created the function by using the readline history, but it was just easier to redefine len.
Oh... it's just occurred to me that you were asking for use-cases for assigning to builtins.len directly, rather than just to len. No, I've never done that -- sorry for the noise.
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.
Ha, well, that's the sort of thing that gives monkey-patching a bad name, surely? Is there a use-case for globally replacing builtins for all modules, everywhere? I suppose that's what you're asking.
The only example I can think of might be the use of mocks for testing purposes, but even there I'd prefer to inject the mock into the module I was testing:
mymodule.len = mylen
But I haven't done much work with mocks, so I'm just guessing.