Control flow is essential in any programming language. Python uses if, elif, and else statements to make decisions in your programs based on conditions.

In this tutorial, you’ll learn:

• The basic structure of if, elif, and else

• How conditions work

• Nested and chained conditions

• Common mistakes

• Tips and tricks

• A complete example at the end

What Is if...else?

Python's if...else statements let you run code based on whether a condition is true or false.

✅ Basic Structure

if condition:
    # code to run if condition is true
elif another_condition:
    # code to run if another_condition is true
else:
    # code to run if no conditions are true

Example 1: Simple if Statement

x = 10
if x > 5:
    print("x is greater than 5")

Output:

x is greater than 5

Example 2: if...else Statement

x = 3
if x > 5:
    print("x is greater than 5")
else:
    print("x is 5 or less")

Example 3: if...elif...else

score = 85

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

Understanding Boolean Conditions

Python evaluates conditions as either True or False.

# Comparisons
x == 5     # True if x equals 5
x != 10    # True if x does not equal 10
x > 3      # Greater than
x < 7      # Less than
x >= 3     # Greater than or equal
x <= 9     # Less than or equal

# Logical operators
x > 3 and x < 7     # True if both are True
x == 5 or x == 10   # True if either is True
not x == 5          # True if x is NOT 5

Nested if Statements

You can place an if inside another if:

age = 20
has_id = True

if age >= 18:
    if has_id:
        print("Access granted.")
    else:
        print("ID required.")
else:
    print("Access denied.")

Chained Conditions

You can use logical operators (and, or, not) to write complex conditions in a single line.

x = 25
if x > 10 and x < 50:
    print("x is between 10 and 50")

One-Liner if...else (Ternary Operator)

You can write simple if...else expressions in one line:

age = 18
status = "Adult" if age >= 18 else "Minor"
print(status)

Common Pitfalls

Tips

• Use elif to avoid unnecessary nesting.

• Always cover all logical cases with else as a fallback.

• Use parentheses () for clarity in complex conditions.

• Use comments to explain condition logic for beginners.

• Test edge cases (e.g., ==, >=, <=) to avoid logic bugs.

Complete Example: Voting Eligibility

age = int(input("Enter your age: "))
citizen = input("Are you a citizen? (yes/no): ").lower()

if age >= 18:
    if citizen == "yes":
        print("You are eligible to vote.")
    else:
        print("You must be a citizen to vote.")
else:
    print("You must be at least 18 years old to vote.")

What’s Next?

After mastering if...else, explore:

• While and for loops

• Logical operators in depth

• Exception handling with try...except

• Functions to modularize your logic

Practice Challenge

Task: Write a program that checks if a number is positive, negative, or zero.

number = float(input("Enter a number: "))

if number > 0:
    print("Positive")
elif number < 0:
    print("Negative")
else:
    print("Zero")