Python while loop

Filed Under: Python

In this tutorial we will cover basics of python while loop. In the previous tutorial, we learned about Python for loop.

Python while loop

Python while loop is used to repeatedly execute some statements till the condition is true. So the basic structure of python while loop is:


While condition :
	#Start of the statements
	Statement
	. . . . . . .
	Statement
	#End of the Statements
else :
	#this scope is optional
        #This statements will be executed if the condition
	#written to execute while loop is false

For example the following code will give you some idea about while loop. In this example, we are printing numbers from 1 to 4 inside loop and 5 in outside of the loop


cnt=1 #this is the initial variable
while cnt < 5 :
        #inside of while loop
        print (cnt),
        print ("This is inside of while loop")
        cnt+=1;
else :
        #this statement will be printed if cnt is equals to 5
        print (cnt),
        print("This is outside of while loop")

Output
python while loop

In the example of for loop tutorial we print each letters from words. We can implement that code use while loop. The following code will show you that.


word="anaconda"
pos=0 #initial position is zero
while pos < len(word) :
	print (word[pos])
	#increment the position after printing the letter of that position
	pos+=1 

Output
python while loop example

An interesting fact about loop is if you implement something using for loop, you can implement that in while loop too. Try to implement examples shown in for loop tutorial in while loop.

Python Nested while loop

You can write while loop inside another while loop. Suppose you need to print a pattern like this

    1
    1 2
    1 2 3
    1 2 3 4
    1 2 3 4 5

The following code will illustrate how to implement that using nested while loop.


line=1 #this is the initial variable
while line <= 5 :
        pos = 1
        while pos < line:
 
                #This print will add space after printing the value
                print pos,
                
                #increment the value of pos by one
                pos += 1
        else:
                #This print will add newline after printing the value
                print pos
        
        #increment the value of line by one
        line += 1

Python while loop infinite problem

Since while loop will continue to run until the condition becomes false, you should make sure it does otherwise program will never end. Sometimes it can come handy when you want your program to wait for some input and keep checking continuously.


var = 100
while var == 100 :  # an infinite loop
   data = input("Enter something:")
   print ("You entered : ", data)

print ("Good Bye Friend!")

If you run above program, it will never end and you will have to kill it using Ctrl+C keyboard command.


>>> 
================= RESTART: /Users/pankaj/Desktop/infinite.py =================
Enter something:10
You entered :  10
Enter something:20
You entered :  20
Enter something:
Traceback (most recent call last):
  File "/Users/pankaj/Desktop/infinite.py", line 3, in <module>
    data = input("Enter something:")
KeyboardInterrupt
>>> 

That’s all about python while loop example tutorial. For any queries please comment below.

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