Python - Decision Making

Python's decision making functionality is in its keywords − if..elif...else. The if keyword requires a boolean expression, followed by colon (:) symbol. The colon (:) symbol starts an indented block. The statements with the same level of indentation are executed if the boolean expression in if statement is True. If the expression is not True (False), the interpreter bypasses the indented block and proceeds to execute statements at earlier indentation level.

Decision structures evaluate multiple expressions which produce TRUE or FALSE as outcome. You need to determine which action to take and which statements to execute if outcome is TRUE or FALSE otherwise.

Following is the general form of a typical decision making structure found in most of the programming languages −

Decision making statements in Python

Python programming language assumes any non-zero and non-null values as TRUE, and if it is either zero or null, then it is assumed as FALSE value.

Python programming language provides following types of decision making statements. Click the following links to check their detail.

Sr.No. Statement & Description
1 if statements

An if statement consists of a boolean expression followed by one or more statements.

2 if...else statements

An if statement can be followed by an optional else statement, which executes when the boolean expression is FALSE.

3 nested if statements

You can use one if or else if statement inside another if or else if statement(s).

Let us go through each decision making briefly −

Single Statement Suites

If the suite of an if clause consists only of a single line, it may go on the same line as the header statement.

Here is an example of a one-line if clause −


var = 100
if ( var == 100 ) : print ("Value of expression is 100")
print ("Good bye!")

When the above code is executed, it produces the following result −

Value of expression is 100
Good bye!