Peter Otten wrote: > 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
How do you guarantee that any object of a class has a specific set of attributes? Rui Maciel -- http://mail.python.org/mailman/listinfo/python-list
