Iterate over instances of an ITERABLE class

Question

I have defined the following class

class Person(object):        
    _counter = 0
    _instances = []

    def __init__(self, nam):
        self.name = nam
        self._instances.append(self)
        self._id = Person._counter + 1
        Person._counter+=1        

    def __repr__(self):
        return f'{self._id} : Person({self.name})'    

    def __iter__(self):
        return self

    def __next__(self):
        pass

    @classmethod
    def iterate(cls):
        return [p for p in Person._instances]

I can iterate over the instances of this class with

[p for p in Person._instances]

I would like to learn how it is possible to arrive at the same result by calling

[p for p in Person]

I have searched many similar questions and I tried out several suggested answers, without any luck. I am using Python 3.6 Anaconda x64 and in all the solutions I tested on the interpreter I am getting back

  [p for p in Person]
  TypeError: 'type' object is not iterable

Could you please write exactly how I can execute successfully this [p for p in Person] call to get back the same list as Person.iterate() and Person._instances ?

Answer 1

You can define an __iter__ on the metaclass to make the metaclass instance (i.e. Person) iterable:

class metaclass(type):
   def __iter__(cls):
       return iter(getattr(cls, '_instances', []))

class Person(metaclass=metaclass):  
    # __metaclass__ = metaclass Python 2
    ...