What exactly are iterator, iterable, and iteration?

Question

What is the most basic definition of \"iterable\", \"iterator\" and \"iteration\" in Python?

I have read multiple definitions but I am unable to identify the exact m

Answer 1

Iterable:- something that is iterable is iterable; like sequences like lists ,strings etc. Also it has either the __getitem__ method or an __iter__ method. Now if we use iter() function on that object, we'll get an iterator.

Iterator:- When we get the iterator object from the iter() function; we call __next__() method (in python3) or simply next() (in python2) to get elements one by one. This class or instance of this class is called an iterator.

From docs:-

The use of iterators pervades and unifies Python. Behind the scenes, the for statement calls iter() on the container object. The function returns an iterator object that defines the method __next__() which accesses elements in the container one at a time. When there are no more elements, __next__() raises a StopIteration exception which tells the for loop to terminate. You can call the __next__() method using the next() built-in function; this example shows how it all works:

>>> s = 'abc'
>>> it = iter(s)
>>> it

>>> next(it)
'a'
>>> next(it)
'b'
>>> next(it)
'c'
>>> next(it)
Traceback (most recent call last):
  File "", line 1, in 
    next(it)
StopIteration

Ex of a class:-

class Reverse:
    """Iterator for looping over a sequence backwards."""
    def __init__(self, data):
        self.data = data
        self.index = len(data)
    def __iter__(self):
        return self
    def __next__(self):
        if self.index == 0:
            raise StopIteration
        self.index = self.index - 1
        return self.data[self.index]


>>> rev = Reverse('spam')
>>> iter(rev)
<__main__.Reverse object at 0x00A1DB50>
>>> for char in rev:
...     print(char)
...
m
a
p
s