List mutation method gotcha - How well known?

[Lie]

On Mar 13, 2:36 pm, "Hendrik van Rooyen" <m... at microcorp.co.za> wrote:
> 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

I think I'll choose 3. Well, no, I suppose the correct behavior
_should_ be undefined (i.e. what it returns is an implementation
details that should not be relied on). The fact that it returns None
is just a "coincidence" that happens to happen every time you tested
it (you can't prove by ignorance)