Eric> I think you can do Eric> mylist = [[]] or somesuch...
That won't do what you want. You've defined a list with a single element (another list). You might have been thinking of something like this: >>> N = 4 >>> M = 5 >>> mylist = [[0.0] * M] * N While to the casual glance it looks like what you want: >>> print mylist [[0.0, 0.0, 0.0, 0.0, 0.0], [0.0, 0.0, 0.0, 0.0, 0.0], [0.0, 0.0, 0.0, 0.0, 0.0], [0.0, 0.0, 0.0, 0.0, 0.0]] assigning to an element of this structure demonstrates its shortcoming: >>> mylist[1][1] = 42.7 >>> print mylist [[0.0, 42.700000000000003, 0.0, 0.0, 0.0], [0.0, 42.700000000000003, 0.0, 0.0, 0.0], [0.0, 42.700000000000003, 0.0, 0.0, 0.0], [0.0, 42.700000000000003, 0.0, 0.0, 0.0]] There is just one copy of [0.0] * M referenced N times. Skip -- http://mail.python.org/mailman/listinfo/python-list