15.12.20 19:07, Mark Polesky via Python-list пише:
> # Running this script....
>
> D = {'a':1}
> def get_default():
> print('Nobody expects this')
> return 0
> print(D.get('a', get_default()))
>
> # ...generates this output:
>
> Nobody expects this
> 1
>
> ###
>
> Since I'm brand new to this community, I thought I'd ask here first... Is
> this worthy of a bug report? This behavior is definitely unexpected to me,
> and I accidentally coded an endless loop in a mutual recursion situation
> because of it. Calling dict.get.__doc__ only gives this short sentence:
> Return the value for key if key is in the dictionary, else default. Nothing
> in that docstring suggests that the default value is evaluated even if the
> key exists, and I can't think of any good reason to do so.
>
> Am I missing something?
You are missed that expressions for function arguments are always
evaluated before passing their values to a function. This is expected
behavior, and I can't remember any programming language in which it's
different.
So dict.get() returns the value of argument default, which is computed
by calling function get_default() before calling dict.get().
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