Question

Given a class that keeps a registry of its Objects:

class Person(object):    __registry = []     def __init__(self, name):        self.__registry.append(self)        self.name = name 

How would I make the following code work (without using Person.__registry):

for personobject in Person:     print personobject 

While researching I found a hint that one could go for a __metaclass__ with a __getitem__-method. Any ideas how this would look like?

Answer 1

You can make your class object iterable with a simple metaclass.

class IterRegistry(type):     def __iter__(cls):         return iter(cls._registry)  class Person(object):     __metaclass__ = IterRegistry     _registry = []      def __init__(self, name):         self._registry.append(self)         self.name = name 

(I have also changed __registry to _registry to make it easier to access from the metaclass). Then,

>>> p = Person('John') >>> p2 = Person('Mary') >>> for personobject in Person: ...     print personobject ... <person.Person object at 0x70410> <person.Person object at 0x70250>