> The first statement is creating a whole new list; Yes but *imo* not quite exactly so. We can't think of 2 lists as of absolutely independent things.
... x = [[0]] ... id(x) 19330632 ... id(x[0]) 19316608 ... z = x + [3] ... id(z) 19330312 ... id(z[0]) 19316608 ... ... z[0] is x[0] # ? True ... x[0][0] = 1 ... ... z[0][0] 1 -- http://mail.python.org/mailman/listinfo/python-list