Le Fri, 12 Feb 2010 17:10:01 -0500, Steve Holden a écrit :
>
> As has already been pointed out, if Python used call by reference then
> the following code would run without raising an AssertionError:
>
> def exchange(a, b):
> a, b = b, a
>
> x = 1
> y = 2
> exchange(x, y)
> assert (x == 2 and y == 1)
>
> Since function-local assignment always takes place in the function
> call's local namespace
I don't think this is related to a difference in parameter passing style.
It's just that assignment ("=") means a different thing in Python than in
non-object languages (or fake-object languages such as C++ or PHP): it
rebinds instead of mutating in-place. If it mutated, you wouldn't have
the AssertionError.
If you mutate in-place:
>>> def exchange(a, b):
... t = a[:]
... a[:] = b
... b[:] = t
...
>>> x, y = [1], [2]
>>> exchange(x, y)
>>> x, y
([2], [1])
Regards
Antoine.
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