Eric Snow <ericsnowcurren...@gmail.com> added the comment:
In Python, multiplication on a list does not make copies of the values in the original list. So what you have done is equivalent to the following: a = [0, 0] b = [a, a] M = [b, b] Hence: >>> M[0] is M[1] True >>> M[0][0] is M[0][1] True >>> M[1][0] is M[1][1] True >>> M[0][0] is M[1][0] True So the following *all* modify the first value in "a": M[0][0][0] = 1 M[1][0][0] = 1 M[0][1][0] = 1 M[1][1][0] = 1 That is why you are seeing the result you reported. Depending on your needs, better solutions include using a list comprehension, spelling out the for loops (for readability), a helper function (for complex problems), or simply spelling out the full list literal instead of composing it. Regardless, I highly recommend using a solution that is easy for a new reader to understand. Even if no one else will read this code, your six-months-from-now self will thank you. :) ---------- nosy: +eric.snow resolution: -> not a bug stage: -> resolved status: open -> closed _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue36450> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
