syntax glitch with +=

[Irmen de Jong]

David Eppstein wrote:
> If L and M are lists, L += M is the same as L.extend(M), right?
> Nope:
> 
> L=[]
> 
> def test1():
>    print L
>    L.extend([1,2])
> 
> def test2():
>    print L
>    L += [3,4]
> 
> One of these two works, the other produces an error.

You're getting
UnboundLocalError: local variable 'l' referenced before assignment
right? This error has nothing to do with a presumed difference
between extend and +=, in this case.

You need to add a 'global' statement. Try:

L=[]

def test1():
    global L
    print L
    L.extend([1,2])

def test2():
    global L
    print L
    L += [3,4]


Irmen