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?
Usually, references get passed around wherever possible. Just putting "col" into the list comprehension like you did will never copy. If you need a copy of a list, you could do "col[:]" or "list(col)". More generally, see the "copy" module. -- Robert Kern [EMAIL PROTECTED] "In the fields of hell where the grass grows high Are the graves of dreams allowed to die." -- Richard Harter -- http://mail.python.org/mailman/listinfo/python-list
