Difference between for loop and while loop in Python

In this article, we will learn about the difference between for loop and a while loop in Python. In Python, there are two types of loops available which are 'for loop' and 'while loop'. The loop is a set of statements that are used to execute a set of statements more than one time. For example, if we want to print "Hello world" 100 times then we have to write a print statement 100 times which is a tedious task but with the help of loops we can do it in just a few lines of code. In this article, we will learn both types of loops separately and then their differences.

For loop in Python

In Python, a 'for loop' is used to iterate over a sequence of items, such as a Python tuple, list, string, or range. The loop will execute a block of statements for each item in the sequence.

Python for Loop Flowchart

Syntax of Python for loop

In the below syntax for is a keyword, var is the variable name, and iterable is an object which can be looped over or iterated over with the help of a for a loop. Objects like tuples, lists, sets, dictionaries, strings, etc. are called iterable. We can also use the range() function in place of iterable.

for var in iterable:

   # statements

Python for Loop (With Examples)

In the below example, we have created a list of items and then iterate through the list using for loop to print the items in the list.

# Create a list of items
items = ['pen', 'notebook',
         'pencil', 'lunch box']

# Run a loop to print
# items in a list
for item in items:
  print(item)
  

Output:

pen
notebook
pencil
lunch box

While Loop in Python

In Python, a while loop is used to repeatedly execute a block of statements while a condition is true. The loop will continue to run as long as the condition remains true.

Python while Loop Flowchart

Syntax of Python While loop

In the while loop condition is written just after the 'while' keyword and then we write the set of statements to perform some task.

while condition:

    # Set of statements

Python while Loop (With Examples)

In this example, we are using a while loop to perform the task that we have done in the example of for loop. Here, after declaring the items list we initialize the index with 0 and store the length of the items list in the variable 'items_len' after that running a while loop in which we have given a condition that runs the loop until the value of the index is less than items_len. Inside the while loop, we print the items of the items list using indexing and increment the value of the index by 1 to iterate over the list. 

# Create a list of items
items = ['pen', 'notebook',
         'pencil', 'lunch box']

# Declare a index
index = 0

# Store length of items list
items_len = len(items)

# Run a loop to print
# items in a list
while index<items_len:
  print(items[index])
  index = index+1

Output:

pen
notebook
pencil
lunch box

When no condition is given in the for and while loop?

In this case, when the condition is not given they will run into an infinite loop.

Python For Loop:

a = [1]
for i in a:
    print("GFG")
    a.append(i)

Python While Loop:

while True:
    print("GFG")

Both of the loops will run for infinite times and print GFG.

Difference between for loop and while loop in Python

Now, we will compare both loops in Python to understand where to use 'for loop' and where to use 'while loop'.

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Article Tags :

• Python

Practice Tags :

• python