Iterable vs Iterator

An iterable is any object that can return an iterator.

It represents a collection of elements that can be looped over.

An iterable does not necessarily track iteration state itself.

Examples of iterables include Lists Tuples Strings Sets Dictionaries

Here numbers is iterable.

An iterator is an object that Returns itself from __iter__() Returns the next value from __next__()

It keeps track of the current position during iteration.

Here it is an iterator.

An iterable can create many iterators, but an iterator can be used only once.

The iterator protocol defines how iteration works in Python.

Any object that follows this protocol can be used in a loop.

The protocol consists of two special methods.

The __iter__() method returns the iterator object itself.

This method is called when iteration begins.

For iterators, __iter__() always returns self.

The __next__() method returns the next value from the iterator.

When no values remain, it raises StopIteration.

After the last value, calling next() again raises an exception.

When a for loop starts, Python performs the following steps internally.

Python calls iter() on the iterable. This returns an iterator. Python repeatedly calls __next__() on the iterator. Each returned value is assigned to the loop variable. When StopIteration is raised, the loop ends gracefully.

Although this looks simple, Python is fully relying on the iterator protocol behind the scenes.