If-Else Statements

Real programs need to react to different situations. A game needs to check whether the player has won. A login page needs to check whether the password is correct. A weather app needs to decide what to display based on temperature. All of these decisions use if-else statements — one of the most important ideas in all of programming.

The if Statement

The simplest decision just checks whether something is true:

temperature = 30

if temperature > 25:
    print("It's a hot day!")

If the condition temperature > 25 is True, the indented block runs. If it is False, Python skips the block entirely.

Adding else

else provides an alternative block that runs when the condition is False:

temperature = 18

if temperature > 25:
    print("It's a hot day!")
else:
    print("It's not that warm today.")

Only one of the two blocks will ever run — they are mutually exclusive.

Adding More Choices with elif

When you have more than two possibilities, use elif (short for "else if") to chain conditions:

score = 75

if score >= 90:
    print("Grade: A")
elif score >= 70:
    print("Grade: B")
elif score >= 50:
    print("Grade: C")
else:
    print("Grade: F")

Python checks each condition from top to bottom and runs the first block whose condition is True. Once a match is found, all remaining elif and else blocks are skipped.

Comparison Operators

To write conditions you need comparison operators:

Nested If Statements

You can place an if statement inside another if block:

is_member = True
age = 16

if is_member:
    if age >= 18:
        print("Full membership benefits.")
    else:
        print("Junior member benefits.")
else:
    print("Please join to access benefits.")

A Practical Example

username = input("Username: ")
password = input("Password: ")

if username == "admin" and password == "pass123":
    print("Login successful.")
elif username == "admin":
    print("Wrong password.")
else:
    print("Unknown user.")