Iterator is an object in python which implements two methods, iter and next. We can iterate over it by using for loop.

class Cubes(object):
    def __init__(self, start, stop):
       self.start = start
       self.stop = stop
    def __iter__(self): return self
    def next(self):
       if self.start >= self.stop:
           raise StopIteration
       current = self.start * self.start*self.start
       self.start += 1
       return current


iterator = Cubes(a, b)

it = Cubes(1,5)  # gives an iterator object which on iteration will give cubes of values 1-4
for cube in it:
    print(cube)

*output*
1
8
27
64

Generator functions are the function which have yield statement instead of return. Unlike the return statement yield gives the next object, each time we call it.
Every Generator is an iterator but not every iterator is a generator. Generator syntax is simpler that iterator.

def cubes(start, stop):
    for i in range(start, stop):
        yield i * I * i


generator = cubes(a, b)

Generator expressions are like list comprehensions. Instead of square bracket, it is enclosed within parenthesis.

generator = (i*i*i for i in range(a, b))

We can iterate over it in a loop.

• Meta class is the class of a class.
• Class definitions create a class name, a class dictionary, and a list of base classes. The metaclass is responsible for taking those three arguments and creating the class.
• Most object oriented programming languages provide a default implementation.
• What makes Python special is that it is possible to create custom metaclasses..