# Revision history [back]

This is a very partial answer, but in a Python crash course (by William Stein I presume, now I can't find the link) I learned this example:

def f(a, L=[]):
L.append(a)
return L


with the following astonishing outputs:

sage: f(2)
[2]
sage: f(5)
[2, 5]
sage: f(4)
[2, 5, 4]


(this is pure Python, Sage is not guilty).

This is a very partial answer, but in a Python crash course (by William Stein I presume, now I can't find the link) I learned this example:

def f(a, L=[]):
L.append(a)
return L


with the following astonishing successive outputs:

sage: f(2)
[2]
sage: f(5)
[2, 5]
sage: f(4)
[2, 5, 4]


(this is pure Python, Sage is not guilty).