While loop with 3 conditions python

Loops are used in programming to repeat a specific block of code. In this article, you will learn to create a while loop in Python.

Video: Python while Loop

What is while loop in Python?

The while loop in Python is used to iterate over a block of code as long as the test expression (condition) is true.

We generally use this loop when we don't know the number of times to iterate beforehand.

Syntax of while Loop in Python

while test_expression:
    Body of while

In the while loop, test expression is checked first. The body of the loop is entered only if the test_expression evaluates to True. After one iteration, the test expression is checked again. This process continues until the test_expression evaluates to False.

In Python, the body of the while loop is determined through indentation.

The body starts with indentation and the first unindented line marks the end.

Python interprets any non-zero value as True. None and 0 are interpreted as False.

Flowchart of while Loop

Example: Python while Loop

# Program to add natural
# numbers up to 
# sum = 1+2+3+...+n

# To take input from the user,
# n = int(input("Enter n: "))

n = 10

# initialize sum and counter
sum = 0
i = 1

while i <= n:
    sum = sum + i
    i = i+1    # update counter

# print the sum
print("The sum is", sum)

When you run the program, the output will be:

Enter n: 10
The sum is 55

In the above program, the test expression will be True as long as our counter variable i is less than or equal to n (10 in our program).

We need to increase the value of the counter variable in the body of the loop. This is very important (and mostly forgotten). Failing to do so will result in an infinite loop (never-ending loop).

Finally, the result is displayed.

While loop with else

Same as with for loops, while loops can also have an optional else block.

The else part is executed if the condition in the while loop evaluates to False.

The while loop can be terminated with a break statement. In such cases, the else part is ignored. Hence, a while loop's else part runs if no break occurs and the condition is false.

Here is an example to illustrate this.

'''Example to illustrate
the use of else statement
with the while loop'''

counter = 0

while counter < 3:
    print("Inside loop")
    counter = counter + 1
else:
    print("Inside else")

Output

Inside loop
Inside loop
Inside loop
Inside else

Here, we use a counter variable to print the string Inside loop three times.

On the fourth iteration, the condition in while becomes False. Hence, the else part is executed.

Table of Contents

• What is while loop in Python?
  • Syntax of while Loop in Python
  • Flowchart of while loop
  • Example: Python while Loop
• While loop with else

Python Loops

Python has two primitive loop commands:

• while loops
• for loops

The while Loop

With the while loop we can execute a set of statements as long as a condition is true.

Example

Print i as long as i is less than 6:

i = 1
while i < 6:
  print(i)
  i += 1

Try it Yourself »

Note: remember to increment i, or else the loop will continue forever.

The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1.

The break Statement

With the break statement we can stop the loop even if the while condition is true:

Example

Exit the loop when i is 3:

i = 1
while i < 6:
  print(i)
  if i == 3:
    break
  i += 1

Try it Yourself »

The continue Statement

With the continue statement we can stop the current iteration, and continue with the next:

Example

Continue to the next iteration if i is 3:

i = 0
while i < 6:
  i += 1
  if i == 3:
    continue
  print(i)

Try it Yourself »

The else Statement

With the else statement we can run a block of code once when the condition no longer is true:

Example

Print a message once the condition is false:

i = 1
while i < 6:
  print(i)
  i += 1
else:
  print("i is no longer less than 6")

Try it Yourself »

Can you do a while loop with multiple conditions Python?

Can we put 2 conditions in while loop?

How do you repeat 3 times in Python?

How do you put a condition in a while loop in Python?