Python List Loop Tutorial

In this section we will learn how to iterate through the elements of a List in Python.

Python Iterate List: How to Iterate Through a List in Python?

A List in Python is iterable! That means we can use loops like while and for in order to access the elements of the list and run any necessary operation on them.

Now let’s see how to loop through a list using the for loop:

Python for in List

When using the for-in loop, it goes through the elements of a list and take them one by one until the last element in the list.

Basically, using the for-in loop, there’s no need to use the pair of brackets [] if the iterable object that the loop needs is the list itself.

Example: Python Loop through List via for Loop

list1 = ["John","Jack","Omid","Ellen","Elon","Ian","Jame","Richard"]
for element in list1:
print(element)
Output:
John
Jack
Omid
Ellen
Elon
Ian
Jame
Richard

Python for Loop with Index Number:

The problem that the last example has is that we can’t change the elements of the list if needed! All we got was just the elements of the list! Basically, using this technique we can only read the elements of the list and not modify them!

Now if we want to be able to modify the elements of the list while iterating through them, one option would be to use the len() and range() functions.

Basically, we can use the range() function to produce a sequence of number, use the len() function to get the size of the target list and put that as the argument of the range() function in order to get accurate sequence of numbers and then finally use the produced sequence as the value in the pair of brackets [] in order to access the elements of the target list (either modify or get the values in the list).

Example: Python with for Loop and Index Number

list1 = ["John","Jack","Omid","Ellen","Elon","Ian","Jame","Richard"]
for index in range(len(list1)):
list1[index] = 0
print(list1)
Output:
[0, 0, 0, 0, 0, 0, 0, 0]

Iterate Through List Python via while Loop Example:

list1 = ["John","Jack","Omid","Ellen","Elon","Ian","Jame","Richard"]
num = 0;
size = len(list1)
while num<size:
list1[num] = 0
num +=1
print(list1)
Output:
[0, 0, 0, 0, 0, 0, 0, 0]