Control Flow

In Python, control flow statements allow you to direct the execution of code depending on conditions. This is essential for creating logic in your programs.

Conditional Statements

Python uses if, elif, and else to control the flow based on boolean conditions.

Syntax:

if condition1:
    # do something
elif condition2:
    # do something else
else:
    # do another thing

Example 1: Simple if statement

age: int = 20
if age >= 18:
    print("You are an adult.")

Example 2: if-elif-else with comparison operators

score: int = 85

if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: F")

Using Logical Operators

You can combine multiple conditions using logical operators: - and: True if both conditions are true. - or: True if either condition is true. - not: Inverts the boolean value.

Example 3: Combining conditions

temperature: int = 25
weather: str = "sunny"

if temperature > 20 and weather == "sunny":
    print("Let's go for a picnic!")

Example 4: Using not

is_raining: bool = False

if not is_raining:
    print("You don't need an umbrella.")

Nested If Statements

Python allows you to nest if statements inside each other for more complex logic.

Example 5: Nested conditions

score: int = 88

if score >= 80:
    if score >= 90:
        print("Excellent")
    else:
        print("Very Good")
else:
    print("Needs Improvement")

Indentation is critical in nested ifs — each level must be indented correctly.

Extra Tips and Tools

• Use input() and int() or float() to build interactive programs:

age = int(input("Enter your age: "))
if age < 18:
    print("Access denied.")

• Use pass if a block needs to be empty temporarily:

if age > 100:
    pass  # We'll handle this later

Explore more about Python control flow from the official guide:

Python Control Flow Documentation