Rui Maciel wrote: > Peter Otten wrote: > >> Don't add >> >>>position = [] >> >> to your code. That's not a declaration, but a class attribute and in the >> long run it will cause nothing but trouble. > > Why's that?
Especially with mutable attributes it's hard to keep track whether you are operating on the instance or the class: >>> class Point: ... position = [] ... def __init__(self, x, y, z): ... self.position = [x, y, z] ... >>> a = Point(1, 2, 3) >>> b = Point(10, 20, 30) >>> a.position [1, 2, 3] >>> del a.position >>> a.position [] # did you expect that? >>> del b.position >>> b.position.extend(["did you expect that?"]) >>> a.position ['did you expect that?'] >>> del a.position Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: position -- http://mail.python.org/mailman/listinfo/python-list
