Python Flow Control : While Loop
What is while loop in Python?
The while loop in Python is used to iterate over a block of code as long as the test expression (condition) is true.
We generally use this loop when we don't know beforehand, the number of times to iterate.
Syntax of while Loop in Python
while test_expression:
Body of while
In while loop, test expression is checked first. The body of the loop is entered only if the
test_expression evaluates to True. After one iteration, the test expression is checked again. This process continues until the test_expression evaluates to False.
In Python, the body of the while loop is determined through indentation.
Body starts with indentation and the first unindented line marks the end.
Python interprets any non-zero value as
True. None and 0 are interpreted as False.Flowchart of while Loop
Example: Python while Loop
When you run the program, the output will be:
Enter n: 10
The sum is 55
In the above program, the test expression will be True as long as our counter variable i is less than or equal to n (10 in our program).
We need to increase the value of counter variable in the body of the loop. This is very important (and mostly forgotten). Failing to do so will result in an infinite loop (never ending loop).
Finally the result is displayed.
True as long as our counter variable i is less than or equal to n (10 in our program).while loop with else
Same as that of for loop, we can have an optional else block with while loop as well.
The else part is executed if the condition in the while loop evaluates to False.
The while loop can be terminated with a break statement. In such case, the else part is ignored. Hence, a while loop's else part runs if no break occurs and the condition is false.
Here is an example to illustrate this.
Output
Inside loop
Inside loop
Inside loop
Inside else
Here, we use a counter variable to print the string Inside loop three times.
On the forth iteration, the condition in while becomes False. Hence, the else part is executed.
Thank you :)
else block with while loop as well.else part is executed if the condition in the while loop evaluates to False.else part is ignored. Hence, a while loop's else part runs if no break occurs and the condition is false.Inside loop three times.False. Hence, the else part is executed.
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