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] but all I get back is the builtin None. What am I doing wrong? I'm using Python v2.6

Answer 1

x.extend(x) does not return a new copy, it modifies the list itself.

Just print x instead.

You can also go with x + x

Answer 2

x.extend(x) modifies x in-place.

If you want a new, different list, use y = x + x.