Loops in Python

 

So far we have seen that Python executes code in a sequence and each block of code is executed once.
Loops allow us to execute a block of code several times.

While Loop

Allows us to execute a block of code several times as long as the condition is

True

.

While Loop Example

The following code snippet prints the next three consecutive numbers after a given number.

Code

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a = int(input())

counter = 0

while counter < 3:

a = a + 1

print(a)

counter = counter + 1

PYTHON

Input

4

Output

5

6

7

Possible Mistakes

1. Missing Initialization

Code

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a = int(input())

while counter < 3:

a = a + 1

print(a)

counter = counter + 1

print("End")

PYTHON

Input

5

Output

NameError: name 'counter' is not defined

2. Incorrect Termination Condition

Code

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a = int(input())

counter = 0

condition = (counter < 3)

while condition:

a = a + 1

print(a)

counter = counter + 1

PYTHON

Input

10

Output

The above code runs into an infinite loop.

While block will keep repeating as the value in condition variable is

True

.

3. Not Updating Counter Variable

Code

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a = int(input())

counter = 0

while counter < 3:

a = a + 1

print(a)

print("End")

PYTHON

Input

10

Output

Infinite Loop

As the value of counter is not updating.