Python: append magic

Question

list.append(x)

Add an item to the end of the list.

Okay. Let's write some code:

x = [[]]*3
x[0].append('foo')
print x

and output is:

[['foo'], ['foo'], ['foo']]

Why?

Better question, where does the "real john doe" come from? I've heard it before off an album and had no idea what it meant — But I'm Not A Wrapper Class, Jan 07 '14 at 13:21

score 1 · Accepted Answer · answered Jan 07 '14 at 13:20

1

x = [[]]*3 Creates a list of length 3 where each element have the same reference. So appending to any element will give this result.

answered Jan 07 '14 at 13:20

M4rtini

1 Answers1