Python doesn't use value semantics for variables but reference semantics: a = [1] b = a
In many languages, you'd now have 2 lists. In Python you still have one list, and both a and b refer to it. Now if you modify the data (the list), both variables will change a.append(2) # in-place modification of the list print b # will print [1,2] If you don't want this, you should make a copy somewhere a = a + [2] or b = a[:] It takes a bit of getting used to, but it is very handy in practice. Read the docs about 'immutable' and 'mutable' types. (I expected this to be a FAQ, but I couldn't quickly find a matching entry) Albert -- http://mail.python.org/mailman/listinfo/python-list
