Function __defaults__

Ken Seehart ken at seehart.com
Sun Apr 24 19:07:02 CEST 2011


On 4/24/2011 2:58 AM, Steven D'Aprano wrote:
> Consider this in Python 3.1:
>
>
>>>> def f(a=42):
> ...     return a
> ...
>>>> f()
> 42
>>>> f.__defaults__ = (23,)
>>>> f()
> 23
>
>
> Is this an accident of implementation, or can I trust that changing
> function defaults in this fashion is guaranteed to work?

This is documented in python 3, so I would expect it to be stable (until 
python 4, that is)
http://docs.python.org/py3k/whatsnew/3.0.html#operators-and-special-methods
http://docs.python.org/py3k/library/inspect.html#types-and-members

The f.__defaults__ attribute was previously known as f.func_defaults (in 
python 2.x), which has been around, documented and stable for quite a while.

So it's probably just as safe as any other monkey patching technique. :)

Best of luck,
Ken




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