Hello again everyone ,
var2[:]=[] has solved my problem, and I don't understand why it is programming by side effect.
I don't think it's bad, look at this, it's what I've done :
def Clear(lvar) lvar[:]=[]
def main (starting class) var1=[] var1.append('a') Clear(var1)
From http://en.wikipedia.org/wiki/Side-effect_(computer_science)
In computer science, a side-effect is a property of a programming language function that it modifies some state other than its return value.
Given this definition, I think you're fine -- clearing the list isn't a side effect of the function; it is the purpose of the function. Hence the function has no return value.[1]
Of course, in this simple case, I wouldn't be likely to write the clear function since the inline code is simpler and has less overhead:
def main()
var1 = []
var1.append('a')
var1[:] = []or, since in this case, you only care about var1, you can just rebind it (and let Python garbage-collect the old list):
def main()
var1 = []
var1.append('a')
var1 = []Steve
[1] Technically, all Python functions without a return statement return None, but for our purposes, we can consider a function like this to have "no return value".
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