Python while loop tutorial.
A loop provides the capability to execute a code block again and again. In python, we have two looping techniques.
- Finite loop – At the start, we can set the maximum number of iterations along with the condition, E.g
for loop
. - Infinite loop – At the start, we can set only a condition. So loop executes as long as the condition is true.
While loop is an indefinite loop type. In this tutorial, we will learn how to use a while loop in a program. Execution flow control (break, continue
keywords).
Syntax and basic example :
Syntax –
while expression:
statement 1 with in loop;
statement 2 with in loop;
....
statement N with in loop;
<code after loop >
maxIteration = 5;
while maxIteration > 0:
maxIteration = maxIteration -1;
print(maxIteration);
print("Code after loop body");
Output ->
4 3 2 1 0 Code after loop body
- An integer variable maxIteration is initialized to five.
- Expression maxIteration > 0, returns true, and control enters the loop body.
- Loop Body executes (maxIteration decrements by one and its value is printed on the console).
- Control reaches the start (
while maxIteration > 0:
) of the loop and the reevaluated. - The code with in loop executes again and again till the expression (
maxIteration > 0
) returning true. - The
maxIteration
, becomes less than zero after 5 iterations. Loop ends and statement (print("Code after loop body");
) just after the body executes.
Multiple Conditions in expressions-
The conditional expression may contain multiple subexpressions with logical operators.
maxIteration = 5;
printIterartion = True;
while maxIteration > 0 and printIterartion :
maxIteration = maxIteration -1;
print(maxIteration);
print("Code after first loop body");
printIterartion = False;
while maxIteration > 0 and printIterartion :
maxIteration = maxIteration -1;
print(maxIteration);
print("Code after second loop body");
Output->
4
3
2
1
0
Code after first loop body
Code after second loop body
Break and Continue:
Loop executes the block and checks the condition. Break and continue are the two statements to alter the flow.
- With the
break
statement control comes out from the body of the loop. - Once the break is encountered, the execution jumps to the first statement after the loop.
maxIteration = 5;
while maxIteration > 0:
maxIteration = maxIteration -1;
if maxIteration == 2:
break;
print(maxIteration);
print("Code after first loop body");
4 3 Code after first loop body
- Continue statement is to jump to the start of the loop.
maxIteration = 5;
while maxIteration > 0:
maxIteration = maxIteration -1;
if maxIteration == 2:
continue;
print(maxIteration);
print("Code after first loop body");
4 3 1 0 Code after first loop body