So, here I was thinking "oh, this is a nice, easy way to initialize a 4D matrix" (running 2.7.3, non-core libs not allowed):
m = [[None] * 4] * 4 The way to get what I was after was: m = [[None] * 4, [None] * 4, [None] * 4, [None * 4]] (Obviously, I could have just hardcoded the initialization, but I'm too lazy to type all that out ;)) The behaviour I encountered seems a little contradictory to me. [None] * 4 creates four distinct elements in a single array while [[None] * 4] * 4 creates one distinct array of four distinct elements, with three references to it: >>> a = [None] * 4 >>> a[0] = 'a' >>> a ['a', None, None, None] >>> m = [[None] * 4] * 4 >>> m[0][0] = 'm' >>> m [['m', None, None, None], ['m', None, None, None], ['m', None, None, None], ['m', None, None, None]] Is this expected behaviour and if so, why? In my mind either result makes sense, but the inconsistency is what throws me off. Demian Brecht @demianbrecht http://demianbrecht.github.com -- http://mail.python.org/mailman/listinfo/python-list
