Skip to content
Related Articles

Related Articles

Ways to increment Iterator from inside the For loop in Python
  • Difficulty Level : Basic
  • Last Updated : 12 Feb, 2021

For loops, in general, are used for sequential traversal. It falls under the category of definite iteration. Definite iterations mean the number of repetitions is specified explicitly in advance. But have you ever wondered, what happens, if you try to increment the value of the iterator from inside the for loop. Let’s see with the help of the below example.
Example:
 

Python3




lis = [1, 2, 3, 4, 5]
 
for i in range(len(lis)):
     
    print(lis[i])
    i += 2

Output:
 

1
2
3
4
5

The above example shows this odd behavior of the for loop because the for loop in Python is not a convention C style for loop, i.e., for (i=0; i<n; i++) rather it is a for in loop which is similar to for each loop in other languages. However, there are few methods by which we can control the iteration in the for loop. Some of them are –
 

  • Using While loop: We can’t directly increase/decrease the iteration value inside the body of the for loop, we can use while loop for this purpose.
    Example:
     

Python




# Using while loop
 
lis = [1, 2, 3, 4, 5]
i = 0
 
while(i < len(lis)):
    print(lis[i], end = " ")
     
    # Changing the value of
    # i inside the loop will
    # change it's value at the
    # time of checking condition
    i += 2
    
  • Output: 
     
1 3 5
  •  
  • Using another variable: We can use another variable for the same purpose because after every iteration the value of loop variable is re-initialized.
    Example: 
     

Python




# Using for loop
 
lis = [1, 2, 3, 4, 5]
 
i = 0
 
for j in range(len(lis)):
 
    # Terminating condition for i
    if(i >= len(lis)):
        break
     
    print(lis[i], end = " ")   
    i += 2
  • Output: 
     
1 3 5
  •  
  • Using Range Function: We can use the range function as the third parameter of this function specifies the step.
    Note: For more information, refer to Python range() Function.
    Example:
     

Python3




# Using for loop
 
lis = [1, 2, 3, 4, 5]
 
for i in range(0, len(lis), 2):
     
    print(lis[i], end = " ")   
  • Output:
     
1 3 5
  •  

 

Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course.




My Personal Notes arrow_drop_up
Recommended Articles
Page :