If I use concatenation + instead of multiplication * then I get the result that Jiri expected:
>>> L = [[]] + [[]] >>> L[1].append(1) >>> L [[], [1]] With * both elements are changed: >>> L = [[]] * 2 >>> L[1].append(1) >>> L [[1], [1]] Alex Martelli says in his excellent Nutshell book that + is concatenation and that "n*S is the concatenation of n copies of S". But it seems not so. Surely, from a logical point of view, S + S should be the same as S * 2? Peter The excellent Martelli Python Nutshell says that multiplication S*n is "the concatenation of n copies of S" so S+S and S*2 would be expected to be the same. It seems though that they are not but that * creates a list Jiri Barton wrote: > Hi everyone, > > I have a problem with initialization. > >>>>a, b = [[]]*2 >>>>a.append(1) >>>>b > > [1] > > Why is this? Why does not this behave like the below: > > >>>>a, b = [[], []] >>>>a.append(1) >>>>b > > [] > > And, just to add to my confusion: > > >>>>[[]]*2 > > [[], []] > >>>>[[], []] == [[]]*2 > > True > > Thanks in advance for the explanation. > jbar > > > BTW, if it matters... > Python 2.4.1 (#2, Mar 30 2005, 20:41:35) > [GCC 3.3.5 (Debian 1:3.3.5-8ubuntu2)] on linux2 > > > -- http://mail.python.org/mailman/listinfo/python-list
