On 3 May 2005 10:42:43 -0700, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > I'm new to python. I tried doing this > > >>> x = [[]] * 3 > >>> print x > [ [] [] [] ] > >>> x[0].append( 2 ) > [ [2] [2] [2] ] > > I confused with the last line output. I actually expected something > like > > [ [2] [] [] ] > > Can anyone give me an explanation. help!! >
All three lists refer to the same object: >>> x = [[]]*3 >>> x [[], [], []] >>> #the id function returns the memory address of an object ... >>> [id(a) for a in x] [168612012, 168612012, 168612012] So, when you change the first object, you change all of them. This is a common gotcha with mutable objects (lists and dictionaries, mostly). To get three independant lists, try a list comprehension: >>> y = [[] for i in range(3)] >>> y [[], [], []] >>> [id(b) for b in y] [168611980, 168612300, 168611916] Or, replace x[0] with a new list, instead of modifying the one already there: >>> x[0] = [2] >>> x [[2], [], []] Peace Bill Mill bill.mill at gmail.com -- http://mail.python.org/mailman/listinfo/python-list
