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Python iter() method

  • Last Updated : 11 Apr, 2022

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

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

  • Iteration object remembers iteration count via 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() Example

Example 1: Python iterate list

Python3




# Python3 code to demonstrate
# working of iter()
 
# initializing list
lis1 = [1, 2, 3, 4, 5]
 
# printing type
print("The list is of type : " + str(type(lis1)))
 
# converting list using iter()
lis1 = iter(lis1)
 
# printing type
print("The iterator is of type : " + str(type(lis1)))
 
# using next() to print iterator values
print(next(lis1))
print(next(lis1))
print(next(lis1))
print(next(lis1))
print(next(lis1))
Output
The list is of type : <class 'list'>
The iterator is of type : <class 'list_iterator'>
1
2
3
4
5

Example 2: Python iterate list with index

Python3




# Python 3 code to demonstrate
# property of iter()
 
# initializing list
lis1 = [1, 2, 3, 4, 5]
 
# converting list using iter()
lis1 = iter(lis1)
 
# prints this
print("Values at 1st iteration : ")
for i in range(0, 5):
    print(next(lis1))
 
# doesn't print this
print("Values at 2nd iteration : ")
for i in range(0, 5):
    print(next(lis1))

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

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