List mutation method gotcha - How well known?

[Hendrik van Rooyen]

Hi,

I am surprised that it took me so long to bloody my nose on this one.

It must be well known - and I would like to find out how well known.

So here is a CLOSED BOOK multiple choice question - no RTFM, 
no playing at the interactive prompt:

Given the following three lines of code at the interactive prompt:

foo = [1,2,3,4]
x = foo.append(5)
print x

What will be the output (choose one):

1)  [1,2,3,4]
2)  [1,2,3,4,5]
3)  That famous picture of Albert Einstein sticking out his tongue
4)  Nothing - no output
5)  None of the above

I undertake to summarise answers posted to complete this "survey".

- Hendrik