Hello
I stumbled on something I found surprising. I'm using standard python
(cpython, I guess) 2.7 on openSuse 13.1.
Consider the function
In [2]: def f(x,y=[]):
...: print y
...: y.append(x)
...: return x
This is the output of repeated calls to this function:
In [3]: f(1)
[]
Out[3]: 1
In [4]: f(2)
[1]
Out[4]: 2
In [5]: f(3)
[1, 2]
Out[5]: 3
So, the function seems to keep the value of the optional argument y over
repeated calls. I was expecting that the optional argument, if not set
explicitly in the calling command, would always assume the default value
(the empty list), at every call.
I guess it has something to do with the mutability of the optional
argument (in this case, a list), because it works as I expect if the
optional argument is an int, for instance:
In [8]: def g(x,y=0):
...: print y
...: y += x
...: return x
...:
In [9]: g(1)
0
Out[9]: 1
In [10]: g(2)
0
Out[10]: 2
(No memory of previous calls to the function.)
Is there a rationale for this behavior?
Thanks for any help,
Ze
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