While loop in Python

While loop

While loops are used when a block of code needs to be executed as long as the specific condition is True. 

Syntax:

while condition:

    // code to be executed

Before we see the examples of while loop, Below are the couple of points to remember. 

• If the condition is not satisfied (or False) on the first instance, code inside the loop will not be executed at all. 
• If the condition is satisfied (or True) for every iteration, Loop will run infinitely. 

Let's have a look at the simple example. 

In the above example, 

• Line - 1: Creating or Initializing variable to use in the condition or loop. 
• Line - 2: while 'condition', We are using condition 'i < 10'. Loop would repeat as long as the value of 'i' is less than 10. 
• Line - 3: print statement to print the value of 'i'. This is usually replaced with the required action in the program. 
• Line - 4: Incrementing the value of 'i' by '1'. Incrementing, Decrementing or Amending the value of the variable used in the condition is essential is most of the cases. Otherwise, there is a risk of loop running infinitely. 

We can use either True or False instead of condition. However, mentioning 'True' would cause the loop to run infinitely and 'False' would cause the loop to not run at all. 

In this example, while loop will run infinitely. 

break statement

In the above example, loop is run infinitely. We can use the break statement to exit from the loop. 

No statement in the while loop is executed after the break statement.

In the above example, loop would be repeated until the break statement is executed (i.e., when condition 'i == 10' is satisfied).

continue statement

break statement would terminate the loop execution. But, if we need to skip the processing for that particular iteration and continue with the loop, continue statement can be used. 

None of the following statements would be executed in that iteration and next iteration would continue normally. 

In the above example, 'print' statement would not be executed when value of 'i' becomes '5'. 

pass statement

pass statement works like a place holder if no specific operations is required and is mandatory by syntax. 

In the above example, No action is required when value of 'i' becomes '5'. We can use 'pass' statement.

else statement

Else in while loop isn't exactly same as if-else. Instead this is executed once the while loop is completed. 

In the above example, statements in the else block are executed once the while loop is completed. All the numbers from 0 to 9 would be printed followed by "While loop is Completed" in else block.

One thing to remember here is 'else' part would only be executed if the while loop is executed completely and not terminated by using 'break' statement. If break statement is executed, else part wouldn't be executed.

In the above example, statement in the else block would not be executed as the break statement is run.

Nested while loops

Like Nested if, while loops can be nested in other while loop. 

In the above example, 

• Line - 3: First while loop is repeated as long as 'i < 3' is satisfied and loop will be terminated once i becomes '3'. 
• Line - 4: Variable 'j' is created with '0'. This is executed for every iteration of the previous loop.
• Line - 5: Second while loop is repeated as long as 'j < 3' is satisfied and loop will be terminated once j becomes '3'.
• This loop is run for every iteration in the first loop. 

Result would be printed like below. 

One thing to note here is, break and continue statements would only apply to the loop the statement is executed on (i.e., closest loop). 

In the above example, break statement would terminate the inner loop and outer loop would still continue normally. 

Hope the above was a bit of help to understand the while loops in Python. 

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