is this a bug or what?

[Justin Sheehy]

"I.J." <shiver at yubc.net> writes:

>>>> M=[[0]*3]*3
>>>> M
> [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>>> M[1][1]=1
>>>> M
> [[0, 1, 0], [0, 1, 0], [0, 1, 0]]
>
> Is this new age math?

No, and it isn't a bug either.

You made a list with three references to the same list in it.  Then
you modified the list that you had three references to.

See also the FAQ:

http://www.python.org/doc/FAQ.html#4.50

-Justin