def args idiom and signatures

[Michel Pelletier]

Emile van Sebille wrote:
> 
> In /F's Standard Python Library I spotted:
> 
>     def _d(y, m, d, days=(0, 31, 59, ..., 334, 365)):
> 
> where the balance of the function relies on days having this value.
> 
> Trying to understand why it may be an argument vs defined within
> the function, I suspect that as the def is only processed to bytecode
> once, whereas an in-line assignment would be re-processed with
> each execution, that the decision is performance based.

You are correct.  There are caveats, however, for instance, it is highly
recommened that these objects be used in a read-only fasion in a
multi-threaded program (or use locks).
 
> Now, in light of the various discussions pertaining to function
> signatures, it seems that this idiom presents a particular problem.

What problem is that?
 
> Various munging of the name or introduction of a static type keyword
> may help address this, but I'm curious if this common usage and
> what people's thoughts are.

Zope uses this all time time, I find it quite useful.

-Michel