Appending a list to itself in Python

Question

I want to attach a list to itself and I thought this would work:

x = [1,2]
y = x.extend(x)
print y

I wanted to get back [1,2,1,2]

Answer 1

If you want a new copy of the list try:

x = [1,2]
y = x + x
print y # prints [1,2,1,2]

The difference is that extend modifies the list "in place", meaning it will always return None even though the list is modified.