Iterator

Iterator is an object that can loop over iterable objects. We can use Iterator in for loops. A list is a well known Iterator.

Implementaion

An object can be a Iterator, if we implement two methods:

  1. __iter__ - returns the object itself.
  2. __next__ - returns the next values and raises StopIteration exception when all objects are looped.

Generator

Generator functions allow you to declare a function that behaves like an iterator.

Implementaion

Method 1

A simple and easy way to create a Generator is to replace a return statement with a yield statement in a function.

The difference is that while a return statement terminates a function entirely, yield statement pauses the function saving all its states and later continues from there on successive calls.

Method 2

An object can be a Generator, if we implement __next__ method.

Note: In the above method the yield statement internally generated the __iter__ and __next__ methods.

Method 3

Generator expressions provide an additional shortcut to build generators out of expressions similar to that of list comprehensions.

Notes

Every generator is an iterator, but not vice versa.