flyaflya wrote: > Robert Kern wrote: > >> flyaflya wrote: >> >>> from random import * >>> >>> col = [0 for i in range(10)] >>> a = [col for i in range(10)] >> >> >> >> This is the problem. The list "a" now has ten references to the same >> object "col". They are not copied. >> >>> seed() >>> for i in range(10): >>> for j in range(10): >>> a[i][j] = randint(0, 100) >> >> >> >> So every time you index into "a[i][j]" you are always getting "col[j]". >> > thanks,I see,I know about reference and copy,but when is it a copy?when > a reference?how can I get a copy when need? I find the answer on <cook book> chapter4.5,it's a practical book for the newbies like me,maybe many newbie using c/c++ would make such mistake -- http://mail.python.org/mailman/listinfo/python-list
