YAI: syntax for preset locals without using dummy args with d efaults
tdelaney at avaya.com
Mon Jan 13 02:09:53 CET 2003
> From: Skip Montanaro [mailto:skip at pobox.com]
> Bengt> Right now we often see
> Bengt> def foo(x, y=default, z=some_expression):
> Bengt> ...
> This is just a performance hack and should be addressed by
> other means,
> e.g., more efficient access to global variables. See, for
> example, PEPs 266
> and 267. I believe other not-yet--PEPped proposals have been
> floated as
Well, in *some* circumstances (very rare) it's not just a performance hack.
Specifically, if globals() goes away for some reason, you may not be able to
look up the name anymore. Binding it to via a default value allows you to
keep the reference.
In nearly every case though, doing this is a Bad Thing(TM). The *only* case
I've ever seen this is in my coverage module, where I blow everything away
in order to set up a "clean" environment for the module to be covered and
restore it afterwards. The module to be covered also thinks it's the
__main__ module ... ;) Plus the default values are *also* a performance
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