Antoon Pardon wrote:
> The question is, should we consider this a problem. Personnaly, I
> see this as not very different from functions with a list as a default
> argument. In that case we often have a list used as a constant too.
>
> Yet python doesn't has a problem with mutating this list so that on
> the next call a 'different' list is the default. So if mutating
> a list used as a constant is not a problem there, why should it
> be a problem in your example?
>
Are you serious about that?
The semantics of default arguments are quite clearly defined (although
suprising to some people): the default argument is evaluated once when the
function is defined and the same value is then reused on each call.
The semantics of list constants are also clearly defined: a new list is
created each time the statement is executed. Consider:
res = []
for i in range(10):
res.append(i*i)
If the same list was reused each time this code was executed the list would
get very long. Pre-evaluating a constant list and creating a copy each time
wouldn't break the semantics, but simply reusing it would be disastrous.
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