Python iter() method

python iter() method returns the iterator object, it is used to convert an iterable to the iterator.

iter Function in Python Syntax

The iter() method in Python has the following syntax:

Syntax : iter(obj, sentinel)

Parameters : 

• obj : Object which has to be converted to iterable ( usually an iterator ).
• sentinel : value used to represent end of sequence.

Returns : Iterator object

Properties of Iterators

• The iteration object remembers the iteration count via the internal count variable.
• Once the iteration is complete, it raises a StopIteration exception and the iteration count cannot be reassigned to 0.
• Therefore, it can be used to traverse the container just once.

Python iter() Function Examples

Let us see a few examples of the iter function in Python.

Python Iterate List using iter Function

In this example, we will take a Python List and use the iter() method on it and convert it into an iterator.

The list is of type : <class 'list'>
The iterator is of type : <class 'list_iterator'>
1
2
3
4
5

Python Iterate List with Index

In this example, we will take a Python List and use the iter() function on it. Then convert it into an iterator and print its value using the next() function.

In the second iteration, we again try to print the values using the next() function. But this time it generated an error because in the first iteration, the iterator has already reached its limit and there are no more values in it to print.

Expected Output: 

Values at 1st iteration : 
1
2
3
4
5
Values at 2nd iteration : 

Actual Exception (Error): 

Traceback (most recent call last):
  File "/home/0d0e86c6115170d7cd9083bcef1f22ef.py", line 18, in 
    print (next(lis1))
StopIteration