Learning python - If Statements

If statements

An if statement lets your program make decisions. Python checks a condition, and if it’s true, the code underneath runs.

Use == to compare values (two equals signs), and always end the line with a colon. Anything inside the if block must be indented.

age = 20

if age >= 18:
    print("You can create an account.")
else:
    print("You must be 18 or over.")

Nested if statements

A nested if is simply an if statement inside another if statement. This is useful when you need more than one check.

password = "secret123"
entered = input("Enter your password: ")

if entered != password:
    print("Incorrect password.")
else:
    print("Login successful.")
    two_factor = input("Enter your 2FA code: ")

    if two_factor != "1234":
        print("Incorrect 2FA code.")
    else:
        print("Access granted.")

elif

elif means "else if". It lets you check several conditions one after another.

temperature = int(input("What is the temperature? "))

if temperature < 0:
    print("It is freezing today.")
elif temperature < 15:
    print("It is cold outside.")
elif temperature < 25:
    print("The weather is mild.")
else:
    print("It is warm today.")

Not equals (!=)

Use != to check whether two values do not match.

answer = input("Enter Y or N: ")

if answer != "Y":
    print("You did not enter Y.")

and

Use and when both conditions must be true.

age = 25
has_id = True

if age >= 18 and has_id:
    print("Entry allowed.")

or

Use or when at least one condition needs to be true.

day = input("Enter a day: ")

if day == "Saturday" or day == "Sunday":
    print("It is the weekend!")
else:
    print("It is a weekday.")

A common mistake with `or`

Beginners sometimes write this:

if choice == "A" or "B":  # This always evaluates as True

The correct way is:

if choice == "A" or choice == "B":

Or shorter:

if choice in ["A", "B"]:

Understanding the difference between `else` and `elif`

It helps to think about how many outcomes your code needs to handle.

Use `else` when there are only two possibilities

else covers "anything that wasn’t caught above".

if code == "1234":
    print("Access granted.")
else:
    print("Incorrect code.")

There are only two outcomes:

Correct code
Anything else

Use `elif` when you have more than two options

Each elif checks for an extra, separate condition.

if grade >= 90:
    print("A")
elif grade >= 80:
    print("B")
elif grade >= 70:
    print("C")
else:
    print("Below C")

Quick summary

if → first check
elif → extra checks
else → everything else

Example

status = input("Enter status: online, away, or offline: ")

if status == "online":
    print("User is active.")
elif status == "away":
    print("User is idle.")
else:
    print("User is offline.")

Vivienne Reay