Can I iterate over a class in Python?

Question

I have a class that keeps track of its instances in a class variable, something like this:

class Foo:
    by_id = {}

    def __init__(self, id):
        sel         


        

Answer 1

Magic methods are always looked up on the class, so adding __iter__ to the class won't make it iterable. However the class is an instance of its metaclass, so the metaclass is the correct place to define the __iter__ method.

class FooMeta(type):
    def __iter__(self):
        return self.by_id.iteritems()

class Foo:
    __metaclass__ = FooMeta
    ...