On Apr 11, 10:40 am, [EMAIL PROTECTED] (Alex Martelli) wrote: > wswilson <[EMAIL PROTECTED]> wrote: > > Here is my code: > > > class A(): > > val = 0 > > > def b(item, a): > > a.val = a.val + 1 > > return item + a.val > > > def c(): > > d = [1, 2, 3] > > print [b(item, A()) for item in d] > > > c() > > > I expected this to output [2, 4, 6]. However, it outputs [2, 3, 4] > > which is not what I wanted. I thought that if I passed the A() > > instance in my list comprehension in c(), then the changes I made to > > a.val in b() would be reflected in the A() instance next time the list > > comprehension called b(). But, obviously that is not happening. I'm > > kinda new at python so I may be missing something obvious here. > > Yep: > > a.val = a.val + 1 > > sets in INSTANCE variable a the value computed on the RHS. A.val (the > CLASS variable) is never changed. You're not "passing the class", of > course, but rather an instance of the class. > > To increment A.val, you need to assign to the class variable, or write > some method in class A which assigns to the class variable. If you > want, you can change class A only, leaving all of the rest of your code > untouched, with a property (but then A needs to be newstile), e.g.: > > class A(object): > _val = 0 > def getval(self): return A._val > def setval(self, value): A._val = value > val = property(getval, setval) > > now your code should work as intended: any read access to a.val returns > A._val, and any setting of a.val actually sets A._val, as you appear to > desire. > > Alex
Thanks, that should work well. I appreciate it. -- http://mail.python.org/mailman/listinfo/python-list
