Decision making is anticipation of conditions occurring while execution of the program and specifying actions taken according to the conditions.
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 −
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.
| 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
#!/usr/bin/python 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!