Python While Loop

Loops can execute a code statement multiple time. In Python, the while loop can execute a given statement multiple times if the condition provided to the statement is true.

It is used when we don’t know how many times we want to execute/iterate through a piece of code.

Note Executing through a block of code is called iteration, e.g., if a block of code is executed 2 times, then we say that the block of code is iterated twice.

Code can be iterated indefinite times using a loop, it means that we have no idea how many times the code will be iterated. The while loop is an indefinite loop, let’s see why by having a look at its syntax.

Syntax
The syntax of the while loop is as follows: –

while condition:
statement(s)

Example

Let’s see how the code was executed: –

We set two variables “a” and “i” where “a” was bigger than “i”.
Then, by writing this syntax “while i <= a”, we told the computer that you have to execute the code written below that is “print(a)” until the “i” is smaller than or equal to “a”.
Now we have to change the value of either “i” or “a” to stop the while loop from executing infinite times because “i” will always remain smaller than “a”. This is the reason we wrote “a = a – 1″, now after each iteration, the value of “a” will decrease by 1.

After iterating through the while loop 6 times, the value of “a” becomes equal to 4 which does not satisfy our condition, the while loop breaks itself and the code either ends or moves to next bit of the code.

Note A very important thing to remember about any kind of loop is that it requires an extra variable to run itself and that variable is called indexing variable. In the above example, our indexing variable was “i”.

You can also write while loops in a single line like this –

Example

Different statements are separated using the semicolon (;).

continue And break Statements

Sometimes, we don’t want the statement to execute on a given condition or a range of conditions, we can either use continue to continue executing the upcoming iterations and skip the current iterations or break to stop iterating through the loop if a given condition is met.

continue

Let’s understand it by having an example first –

Example

break

Similarly, for the break statement:

Example

As you can see in the above code that interpreter didn’t execute after “a” became equal to 7. It is used to “break” or exit the loop when a given condition is true.

else Statement in while loop

The “else” statement for the while loop is similar to the “else” of if-else statements which stated that “do this if the condition is not satisfied”. Let’s have an example –

Example

Note The else part of the above code will always be executed unless a break statement exits the while loop.

An Infinite while Loop

A while loop can run forever if the condition remains always truth.

Example

As you can see above, the code never stopped looping through a number of given statements and will go till infinity.

Note To stop a while loop from executing itself infinite times, the indexing variable should come into a state where it does not satisfy a given condition.