Le 21/01/2014 20:19, Chris Angelico a écrit :
On Wed, Jan 22, 2014 at 6:11 AM, Mû <m...@melix.net> wrote:
The function acts as if there were a global variable x, but the call of x
results in an error (undefined variable). I don't understand why the
successive calls of f() don't return the same value: indeed, I thought that
[2,3] was the default argument of the function f, thus I expected the three
calls of f() to be exactly equivalent.
In a sense, there is. The default for the argument is simply an object
like any other, and it's stored in one place.
For cases where you want a mutable default that is "reset" every time,
the most common idiom is this:
def f(x=None):
if x is None: x=[2,3]
x.append(1)
return x
That will create a new list every time, with the same initial contents.
ChrisA
Thank you, thanks everybody,
These were clear and quick answers to my problem. I did not think of
this possibility: the default argument is created once, but accessible
only by the function, therefore is not a global variable, whereas it
looks like if it were at first glance.
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Mû
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