Python uses if keyword to implement decision control. Python’s syntax for executing block conditionally is as below:

Any Boolean expression evaluating to True or False appears after if keyword. USE : symbol and press Enter after the expression to start a block with increased indent. One or more statements written with the same level of indent will be executed if the Boolean expression evaluates to True. To end the block, press backspace to de-dent. Subsequent statements after the block will be executed if the expression is false or after the block if expression is true.

Along with if statement, else clause can also be optionally USED to define alternate block of statements to be executed if the Boolean expression (in if statement) is not true. Following code skeleton shows how else block is used.

There may be situations where cascaded or nested conditional statements are required to be used as shown in the following skeleton:

As you can see, the indentation level of each subsequent block goes on increasing because if block starts after empty else. To avoid these clumsy indentations, we can combine empty else and subsequent if by elif keyword. General syntax of if – elif – else usage is as below:

In this code, one if block, FOLLOWED by one or more elif blocks and one else block at the end will appear. Boolean expression in front of elif is evaluated if previous expression fails. Last else block is run only when all previous expressions turn out to be not true. Importantly all blocks have the same level of indentation.

Here is a simple example to demonstrate the use of elif keyword. The following program computes discount at different rates if the amount is in different slabs.

Output: