Loops in Python

Loops enable us to alter the flow of the program so that instead of writing the same code, again and again, we can repeat the same code a finite number of times. For example, if we need to print the first 10 natural numbers then, instead of using the print statement 10 times, we can print inside a loop that runs up to 10 iterations.

Python provides two ways for executing the loops. While the two ways provide similar basic functionality, they differ in their syntax and condition checking time.

1. for Loop

2. while Loop

1. for Loop

For loops iterate over a given sequence. It is better to use if the number of iterations is known in advance.

numbers = [2, 5, 8, 11]
for number in numbers:
    print(number)

output:

2
5
8
11

We can also use it with the range() function

for number in range(2, 12, 3):
    print(number)

output:

2
5
8
11

2. While Loop

The block of statements is executed while the condition specified in the while loop is True. The while loop is used in the scenario where we don't know the number of iterations in advance.

number = 2
while number < 12:
    print(number)
    number += 3

output:

2
5
8
11

break and continue statements

break is used to exit a for loop or a while loop, whereas continue is used to skip the current block and return to the for or while statement.

for x in range(10):
    if x % 3 == 0:
        continue
    print(x)

output:

1
2
4
5
7
8

x = 0
while x < 10:
    print(x)
    x += 1
    if x > 5:
        break

output:

0
1
2
3
4
5

Use else clause for loops

we can use else for loops. When the loop condition of for or while statement fails then code part in else is executed. If a break statement is executed inside the for loop then the else part is skipped. Note that the else part is executed even if there is a continue statement.

number = 1
while(number < 10):
    if(number % 5 == 0):
        break
    print(number)
    number += 1
else:
    print("Number value equal: " + str(number))

output:

1
2
3
4

for number in range(10):
    if(number % 5 == 0):
        continue
    print(number)
else:
    print("The value equal: " + str(number))

output:

1
2
3
4
6
7
8
9
The value equal: 9

Pass statement

Used to execute an empty loop. The pass statement is useful when you don't write the implementation of a loop but you want to implement it in the future.

for i in range(10):
    pass