<dict>.setdefault()

[Erik Max Francis]

Tino Lange wrote:

> I just realized that <dict>.setdefault *always* executes the second
> argument - even if it's not necessary, because the requested item in
> the first argument exists.
> 
> This is not what I expected - why evaluate the second argument if it's
> not needed? Also this can lead to side-effects!

Because Python doesn't have macros or special forms that look like
functions.  If you see something that looks like a function, it
evaluates all arguments before it calls the function.  Always.  Changing
this would cause confusion, not resolve it.

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