On Fri, Apr 21, 2017 at 11:47:24AM +0200, Justus Schwabedal wrote: > At least I think it's a bug. Maybe it's a feature..
it's indeed a feature. > I possibly found a bug in class __init__ and would like to fix it technically, it's a method. More precisely, it's the constructor method. > So I'm looking for a mentor to help me. > > class Foo: > def __init__(self, bar=[]): > self.list = bar > > spam_1 = Foo() > spam_2 = Foo() > > spam_1.list.append(42) > print(spam_2.list)` the argument `bar` of your method is instanciated at the time you're declaring the method. It's happening once for the the lifetime of the execution of your code. By allocating the `bar` reference into the `self.list` member, you're assigning the same *instance* of that list into the `self.list` member. So everytime you create a new Foo instance, you're actually assigning the same `[]` instance into `self.list` which is why, when you mutate the list, it's happening in all the instances of Foo as well. I hope it makes sense to you ! -- Guyzmo _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
