[Python-ideas] proto-PEP: Fixing Non-constant Default Arguments
rnd at onego.ru
Tue Jan 30 20:48:57 CET 2007
Chris Rebert wrote:
> Roman Susi wrote:
>> I'd liked to say outright that this bad idea which complicates matters
>> P.S. However, I may be wrong. In that case my syntax suggestion would
>> be this:
>> def foo(non_const or ):
>> where  is executed at runtime BECAUSE at def time non_const is
>> somehow True and that is enough to leave  alone.
>> I have not checked, but I believe it is backward compatible.
>> Anyway, could you summarize both contr-argument and this syntax
>> proposal in the PEP?
> I don't quite understand exactly how this would work and would like more
> details on it, but once you've explained it, of course I'd be happy to
> include it in the next draft.
def foo(non_const or ):
is equivalent to
if non_const is None:
none_const = 
And this will be as before:
Also, I thing that programmers should not use subtle difference between
None and other False values, so something like
non_const = none_const or 
is also valid.
Another approach (if you want to pursue the feature) could be
complication to name binding protocol.
a = 
will be as before, but default value assignment could trigger some extra
method. So, you can explicitly regulate your instance reaction to
def __default__(self, old_default):
> - Chris Rebert
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