While Loops in Python

While Loops in Python

While loops are similar to for loops in that they let us repeat a block of code. The difference is that while loops run while a condition is True.

In a while loop, we define the condition, not the number of iterations. The loop stops when the condition is

False

. This is the general syntax of a while loop:

while <condition>:
    youre code

For example:

>>> x = 6

>>> while x < 15:
	print(x)
	x += 1

	
6
7
8
9
10
11
12
13
14
>>> x = 4

>>> while x >= 0:
	print("Hello" * x)
	x -= 1

	
HelloHelloHelloHello
HelloHelloHello
HelloHello
Hello
>>> num = 5

>>> while num >= 1:
	print("*" * num)
	num -= 2

	
*****
***
*

Break and Continue We can also use

break

and

continue

with while loops and they both work exactly the same:

break

stops the while loop immediately.

continue

stops the current iteration and starts the next one. For example:

>>> x = 5

>>> while x < 15:
	if x % 2 == 0:
		print("Even:", x)
		break
	print(x)
	x += 1
    

5
Even: 6
>>> x = 5

>>> while x < 15:
	if x % 2 == 0:
		x += 1
		continue
	print("Odd:", x)
	x += 1

	
Odd: 5
Odd: 7
Odd: 9
Odd: 11
Odd: 13

The

else

Clause We can also add an

else

clause to a while loop. If

break

is found, the

else

clause doesn’t run but if the

break

statement is not found, the

else

clause runs. In the example below, the

break

statement is not found because none of the numbers are even before the condition becomes

False

, so the

else

clause runs.

x = 5

while x < 15:
	if x % 2 == 0:
		print("Even number found")
		break
	print(x)
	x += 2
else:
	print("All numbers were odd")

This is the output:

5
7
9
11
13
All numbers were odd

But in this version of the example, the

break

statement is found and the

else

clause doesn’t run:

x = 5

while x < 15:
	if x % 2 == 0:
		print("Even number found")
		break
	print(x)
	x += 1 # Now we are incrementing the value by 1
else:
	print("All numbers were odd")

The output is:

5
Even number found

Infinite While Loops When we write and work with while loops, we can have something called an “infinite loop.” If the condition is never

False

, the loop will never stop without external intervention. This usually happens when the variables in the condition are not updated properly during the execution of the loop. For example:

>>> x = 5

>>> while x > 2:
	print(x)

	
5
5
5
5
5
5
5
5
5
.
.
.
# The output continues indefinitely

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