Python While Loops
In the previous tutorial, we discussed about loops in general, what they are and their benefits, why we should use them, along with syntax, and the working of the “for” loop. If you haven’t gone through that tutorial till now, I will recommend you to go through that first, so it will be easier for you to learn the concept of while loop, once you have the concept, what loops generally are.
Now, as we know now what loops are and why they are used, in this section, I will go directly towards the working and syntax of while loop along with its comparison with for loop and where to use it.
“A while loop in python runs a bunch of code or statements again and again until the given condition is true when the condition becomes false, the loop terminates its repetition.”
The syntax for a while loop is simple and very much like for loop. We have to use the keyword “while”, along with it, we have to put a condition in parenthesis, and after that, a colon is placed. The condition could be either true or false. Until the condition is true, the loop will keep on executing again and again. If we use a certain condition in our while loop that never becomes false, the program will continue running endlessly until we stop it by force. So, this kind of mistake in our syntax is known as logical/human error.
To terminate an infinite loop, you can press Ctrl+C on your system.
Syntax of while loop:
while codition_is_true:
Code inside the loop bodyFor vs. While:
A “for” statement loop runs until the iteration through, set, lists, tuple, etc., or a generator function is completed. In the case of a while loop, the statement simply loops until the condition we have provided becomes false. We generally use for loops for areas where we are already familiar with the number of iterations and use while loop where the number of iterations are unknown. Because while the loop is solely based on the state of its condition.
Let us understand the concept of the while loop and why we use it in areas where the number of iterations are not defined, or we do not have any idea how many iterations would take place with the help of an example. Suppose that we have created an application for an ATM from where a customer can only withdraw money up to 5000 rupees. Now our condition in the while loop would be to iterate unless the input is between 1 to 5000. So, the condition will be true unless the user inputs a number between 1 to 5000, so the loop will iterate depending upon the time until the user submits the wrong input. The example is a bit rough, but I hope it helps you clear your concepts.
For a While loop to run endlessly, we can pass true or 1 as a condition. 1 is also used in place of writing true as a whole. So, in this case, the condition will never become false, so the program will run endlessly. But these kinds of programs do not output anything because they can never complete their execution.
Example
n = 5
i = 1
while i <= n:
print(i)
i = i+1 # update counter
Output
1
2
3
4
5
2
3
4
5