Python iter() method

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