// B2.1 · ~25 min · Beginner

Decisions with if, elif and else

After this lesson you can write if, elif and else chains that pick the right branch, combine conditions with and, or and not, and predict how Python treats 0, "" and None in a condition.

Lesson 1 of 5 in B2 Control flow

Start of the moduleNext

You will be able to

Write if, elif and else chains, ordered so the right branch runs
Combine comparisons with and, or and not, including chains such as 0 <= x < 10
Predict which values count as false in a condition: None, False, zero and empty collections

Warm-up · Activity 1 of 7
Warm-up from module B1: which of these comparisons are True? Pick all that apply.
Select all that apply.
3 == 3.02 ** 3 == 8'apple' < 'banana'10 != 10

Predict · Activity 2 of 7

Predict before you read on: what does this print?

temperature = 25

if temperature > 30:
    print("hot")
elif temperature > 20:
    print("warm")
elif temperature > 10:
    print("mild")
else:
    print("cold")

coldwarmmildhot

Practice · Activity 3 of 7
Fill in the keyword so that a score of 85 gets "B", and a score of 95 still gets only "A".
```
score = 95
grade = ""

if score >= 90:
    grade += "A"
____ score >= 80:
    grade += "B"
else:
    grade += "C"

print(grade)
```
Your answer score >= 80:
Practice · Activity 4 of 7
or returns one of its operands. What does this print?
```
name = ""
display = name or "guest"
print(display)
```
guestFalseTruename
Practice · Activity 5 of 7
Match each expression to the value it produces.
not 0 — Match for “not 0”
0 <= 5 < 10 — Match for “0 <= 5 < 10”
bool([]) — Match for “bool([])”
"" or "x" — Match for “"" or "x"”
3 and 0 — Match for “3 and 0”
Brain teaser · Activity 6 of 7
Brain teaser. The user typed "no". What does this print?
```
answer = "no"

if answer == "y" or "yes":
    print("continuing")
else:
    print("stopped")
```
stoppedTypeError: cannot compare str with orcontinuingNothing: no branch matches
Apply · Activity 7 of 7
Mini-task. Write a program that reads a year with int(input()) and prints leap or common. A year is a leap year if it divides by 4, except years that divide by 100, unless they also divide by 400. Try 2000, 1900, 2024 and 2023.
Check your work against this list
- Uses % to test divisibility, for example year % 4 == 0
- Combines the three rules with and, or and parentheses in one condition, or with an ordered if and elif chain
- Prints leap for 2000 and 2024, and common for 1900 and 2023
- Prints exactly leap or common, with nothing else on the line

Build it yourself

Read the worked example, then write the exercises. Your code runs in your browser or on your computer and is never uploaded.

Worked example

Museum ticket prices

A museum charges by age: children under 6 go free, visitors under 18 and students pay 6.50 EUR, visitors of 65 or over pay 8 EUR, and everyone else pays 12 EUR. A coupon takes 2 EUR off. The program works out one visitor’s price and prints what kind of ticket it is. Change age, student and coupon at the top and run it again.

main.py

# A museum's ticket rules, checked for one visitor.
age = 16
student = False
coupon = ""  # an empty string: no coupon

if age < 6:
    price = 0.0
elif age < 18 or student:
    price = 6.5
elif age >= 65:
    price = 8.0
else:
    price = 12.0

if coupon:
    price = price - 2
    print("Coupon used:", coupon)

if price == 0:
    print("Free entry")
elif 0 < price <= 7:
    print("Reduced ticket:", price, "EUR")
else:
    print("Full ticket:", price, "EUR")

Run it with

python main.py

Output

Reduced ticket: 6.5 EUR

age < 18 is already True, so Python never looks at student in age < 18 or student.
coupon is an empty string, which is false, so the coupon block is skipped.
0 < price <= 7 is a chained comparison: 0 < price and price <= 7.
The first chain puts age < 6 before age < 18: the other way round, a 4-year-old would pay 6.5.

Change it and run it

Your code (main.py)

Tab indents and Shift+Tab outdents. To leave the editor with the keyboard, press Esc, then Tab.

The first run downloads Python for your browser (up to 6.5 MB) and keeps it cached. Your code stays on your device.

Exercises

Exercise 1 of 2

Weather advice

The program reads a temperature in °C. Print hot above 30, warm from 21 to 30, mild from 11 to 20, and cold for 10 or less. Use one if, elif and else chain, and check the boundaries: 30 is warm, 20 is mild and 10 is cold.

Your code (main.py)

Tab indents and Shift+Tab outdents. To leave the editor with the keyboard, press Esc, then Tab.

The first run downloads Python for your browser (up to 6.5 MB) and keeps it cached. Your code stays on your device.

Hints

Hint 1
Start with the highest range: if temperature > 30. Each elif then only has to check the next boundary down.
Hint 2
"warm from 21 to 30" becomes elif temperature > 20, because anything above 30 already stopped at the first condition.
Hint 3
Four ranges need an if, two elifs and an else. The else catches everything from 10 down.

Show a solution

One way to solve it. Yours can look different and still pass the checks.

temperature = int(input())

if temperature > 30:
    print("hot")
elif temperature > 20:
    print("warm")
elif temperature > 10:
    print("mild")
else:
    print("cold")

Run it on your computer

Install Python 3.14 or newer. Save these files in one folder, open a terminal in that folder, and run the commands below.

main.py

temperature = int(input())

# Print "hot" above 30, "warm" from 21 to 30,
# "mild" from 11 to 20 and "cold" for 10 or less.
print("cold")

test_main.py

from learnrun import run_main


def advice(temperature):
    return run_main(f"{temperature}\n").strip()


def test_hot():
    """31 degrees is hot"""
    got = advice(31)
    assert got == "hot", f"for 31 the program printed {got!r}, expected 'hot'"


def test_warm_and_mild():
    """25 is warm and 15 is mild"""
    got = advice(25), advice(15)
    assert got == ("warm", "mild"), f"for 25 and 15 the program printed {got!r}, expected ('warm', 'mild')"


def test_boundaries():
    """30 is warm, 20 is mild and 10 is cold"""
    got = advice(30), advice(20), advice(10)
    assert got == ("warm", "mild", "cold"), f"for 30, 20 and 10 the program printed {got!r}"


def test_below_zero():
    """-5 is cold"""
    got = advice(-5)
    assert got == "cold", f"for -5 the program printed {got!r}, expected 'cold'"

On macOS and Linux, type python3 wherever these commands say python, as in the first lesson.

Run the program:

python main.py

Run the checks (needs learnrun.py in the same folder):

python learnrun.py test

Download learnrun.py

Exercise 2 of 2

Sign-in check

The program reads a name and then a password, one per line. If the name is empty, print missing name. Otherwise print welcome when the password is open sesame, and wrong password when it is not. Test the empty name with not, not with == "".

Your code (main.py)

Tab indents and Shift+Tab outdents. To leave the editor with the keyboard, press Esc, then Tab.

The first run downloads Python for your browser (up to 6.5 MB) and keeps it cached. Your code stays on your device.

Hints

Hint 1
An empty string is false, so not name is True exactly when the name is empty.
Hint 2
Check the name first: the missing-name message must win even when the password is right.
Hint 3
if not name: … elif password == "open sesame": … else: …

Show a solution

One way to solve it. Yours can look different and still pass the checks.

name = input()
password = input()

if not name:
    print("missing name")
elif password == "open sesame":
    print("welcome")
else:
    print("wrong password")

Run it on your computer

Install Python 3.14 or newer. Save these files in one folder, open a terminal in that folder, and run the commands below.

main.py

name = input()
password = input()

# 1. Empty name: print "missing name".
# 2. Otherwise, password "open sesame": print "welcome".
# 3. Otherwise: print "wrong password".
print("wrong password")

test_main.py

from learnrun import run_main


def sign_in(name, password):
    return run_main(f"{name}\n{password}\n").strip()


def test_welcome():
    """The right password is welcomed"""
    got = sign_in("ada", "open sesame")
    assert got == "welcome", f"for ada / open sesame the program printed {got!r}, expected 'welcome'"


def test_wrong_password():
    """A wrong password is refused"""
    got = sign_in("ada", "open")
    assert got == "wrong password", f"for ada / open the program printed {got!r}, expected 'wrong password'"


def test_missing_name():
    """An empty name is reported first, even with the right password"""
    got = sign_in("", "open sesame")
    assert got == "missing name", f"for an empty name the program printed {got!r}, expected 'missing name'"

On macOS and Linux, type python3 wherever these commands say python, as in the first lesson.

Run the program:

python main.py

Run the checks (needs learnrun.py in the same folder):

python learnrun.py test

Download learnrun.py

Common mistakes

One = in a condition

age = 20
if age = 18:
    print("just an adult")

What Python prints

SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?

Why, and the fix

A single = assigns a value; it is not a question. To compare, write two: if age == 18:. Python refuses to run the file at all, and its message already suggests the fix.

Comparing text from input() with a number

age = "20"  # what input() gives you: a string
if age >= 18:
    print("adult")

What Python prints

TypeError: '>=' not supported between instances of 'str' and 'int'

Why, and the fix

input() always returns a string, even when the user types digits, and Python will not order a string against a number. Convert first: age = int(input()). The error appears only when the line runs, so test your program with real input.

Forgetting to indent the branch

temperature = 35
if temperature > 30:
print("hot")

What Python prints

IndentationError: expected an indented block after 'if' statement on line 2

Why, and the fix

The body of an if is the indented block under it: indentation is how Python knows which lines belong to the branch. Indent it by four spaces. In the editor on this page, Tab inserts four spaces.

Python in the browser: Pyodide 314.0.7, MPL-2.0. Licence and source

Exit ticket

5 questions, no hints. Score 80% or more to complete the lesson.

Finish every activity above to unlock the exit ticket.

Key ideas

At most one branch runs

Python checks the conditions of an if, elif and else chain from the top and runs the first branch whose condition is true. Then it skips the rest of the chain. If no condition is true, the else branch runs, and without an else nothing runs. There can be any number of elif parts, and else is optional. Because the first true condition wins, order matters: put the narrowest test first. score >= 90 must come before score >= 50, or every high score stops at the wider test.

and, or, not and chained comparisons

a and b is true only when both are; a or b when at least one is; not a flips a value. Python stops as soon as it knows the answer: in a or b, b is not even looked at when a is true. and and or return one of their operands, not always True or False, so name or "guest" gives "guest" when name is empty. Comparisons can be chained: 0 <= x < 10 means 0 <= x and x < 10.

Truthy and falsy values

Any value can be a condition. These count as false: None, False, zero in any number type (0, 0.0), and empty strings and collections ("", [], (), {}, set(), range(0)). Nearly everything else counts as true, including "0", " " and [0]; bool(value) shows the result, so bool("") is False. To ask about None itself, write x is None or x is not None. That is why if items: reads as "if the list has something in it". A common slip is answer == "y" or "yes": Python reads it as (answer == "y") or "yes", and the non-empty string "yes" is always true.

Sources

Last reviewed September 29, 2026

Decisions with if, elif and else

Warm-up from module B1: which of these comparisons are True? Pick all that apply.

Predict before you read on: what does this print?

Fill in the keyword so that a score of 85 gets "B", and a score of 95 still gets only "A".

or returns one of its operands. What does this print?

Match each expression to the value it produces.

Brain teaser. The user typed "no". What does this print?

Mini-task. Write a program that reads a year with int(input()) and prints leap or common. A year is a leap year if it divides by 4, except years that divide by 100, unless they also divide by 400. Try 2000, 1900, 2024 and 2023.

Build it yourself

Museum ticket prices

Exercises

Weather advice

Sign-in check

Common mistakes

One = in a condition

Comparing text from input() with a number

Forgetting to indent the branch

Exit ticket

Key ideas

At most one branch runs

and, or, not and chained comparisons

Truthy and falsy values

Sources