Control Flow in Python

Control flow in Python allows you to direct the execution of your program based on conditions you specify. This guide will cover the fundamental concepts of control flow, including if, elif, and else statements, nested conditions, and Boolean logic.

1. if, elif, and else Statements

The if, elif, and else statements are the core of control flow in Python. They allow you to execute certain pieces of code based on whether a condition is true or false.

if Statement

The if statement evaluates a condition (an expression that returns True or False). If the condition is True, the indented block of code following the if statement is executed. If the condition is False, the block of code is skipped.

In this example, since x is indeed greater than 5, the message “x is greater than 5” is printed.

elif Statement

The elif (short for “else if”) statement allows you to check multiple conditions sequentially. If the first if condition is False, Python will check the next elif condition, and so on. If an elif condition is True, its corresponding block of code is executed, and the rest of the elif and else blocks are skipped.

Here, since x is not greater than 15 but is greater than 5, the second message is printed.

else Statement

The else statement provides a block of code that will be executed if none of the preceding if or elif conditions are True.

Since x is not greater than 5, the else block is executed, and “x is 5 or less” is printed.

2. Nested Conditions

You can nest if, elif, and else statements inside one another to create more complex decision-making structures.

In this example:

• The outer if condition checks if x is greater than 10.
• Since x is 20, the condition is True, and the inner if condition is evaluated.
• The inner if condition checks if x is greater than 15, which is also True, so “x is greater than 15” is printed.

3. Boolean Logic

Boolean logic involves combining multiple conditions using logical operators: and, or, and not.

and Operator

The and operator returns True if both conditions are True.

Here, both conditions are True, so “Both conditions are true” is printed.

or Operator

The or operator returns True if at least one of the conditions is True.

In this case, the first condition is True, so “At least one condition is true” is printed.

not Operator

The not operator inverts the value of a condition.

Since x is not greater than 15, the condition not x > 15 is True, and “x is not greater than 15” is printed.

Combining Boolean Logic with Control Flow

You can combine Boolean logic with if, elif, and else statements to create complex control flow.

In this example:

• The first if condition is True, so “Both conditions are true” is printed.
• The elif and else blocks are skipped because the first condition was True.

Summary

Control flow is essential for making decisions in your Python programs. Understanding how to use if, elif, and else statements, nested conditions, and Boolean logic allows you to build sophisticated and dynamic programs. Practice these concepts to become proficient in directing the flow of your code based on various conditions.