In article <40a44d6b-c638-464d-b166-ef66496a0...@l16g2000yqo.googlegroups.com>, "bowman.jos...@gmail.com" <bowman.jos...@gmail.com> wrote:
> Hi, > > I'm trying to write a multi-conditional while statement, and am having > problems. I've broken it down to this simple demo. > > #!/usr/bin/python2.5 > > condition1 = False > condition2 = False > > while not condition1 and not condition2: > print 'conditions met' > if condition1: > condition2 = True > condition1 = True > > > As I understand it, this should print 'conditions met' twice, however, > it only prints it once. It seems that once condition1 is made true, > the whole thing evaluates as true and stops the while loop. Are you perhaps expecting that the "while" condition is tested at the end of the loop? It's not; it is tested at the top of the loop, so, once the condition evaluates as false, the loop exits. This can even result in zero trips: >>> while False: ... print "never" ... >>> Unwinding the snippet above: >>> condition1 = False >>> condition2 = False >>> not condition1 and not condition2 True >>> if condition1: ... condition2 = True ... >>> condition1 = True >>> not condition1 and not condition2 False # -> while loop exits after 1 trip -- Ned Deily, n...@acm.org -- http://mail.python.org/mailman/listinfo/python-list
