Lesson 23

elif - many options

After this lesson: You'll write a program with many roads and understand why the order of the conditions matters.

Video

The video for this lesson is coming soon.

Explanation

if-else is two roads. But what if there are more options? The weather can be freezing, cool, warm or hot. And a match can be won by Ola, by Kuba - or be a draw! That's what elif is for - short for else if. 🌡️

Bajtek's thermometer 🎬

Click Next - you'll see how Python checks the signs in turn, from the top.

Bajtek

❄️🧥🙂🔥

Four kinds of weather

Bajtek builds a thermometer that says what to wear. Below zero - frost ❄️. Below 15 - cool 🧥. Below 25 - warm 🙂. And above - heat 🔥.

Step 1 / 5

The thermometer: 18 degrees

Watch the robot check the signs in turn and stop at the first green one.

🌡️1temp = 18

if temp < 0

3print("Frost ❄️")

❄️

elif temp < 15

5print("Cool 🧥")

🧥

elif temp < 25

7print("Warm 🙂")

🙂

elsein every other case

9print("Heat 🔥")

🔥

Click the arrow - I'll walk the program's path, line by line.

Code

1temp = 18
2if temp < 0:
3    print("Frost ❄️")
4elif temp < 15:
5    print("Cool 🧥")
6elif temp < 25:
7    print("Warm 🙂")
8else:
9    print("Heat 🔥")

Screen

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Your thermometer 🌡️

Type a temperature 🌡️ (e.g. -5, 10 or 30) and press Enter ⏎. Check the limits too: 15 and 25!

🌡️1temp_str = input()

2temp = int(temp_str)

if temp < 0

4print("Frost ❄️")

❄️

elif temp < 15

6print("Cool 🧥")

🧥

elif temp < 25

8print("Warm 🙂")

🙂

elsein every other case

10print("Heat 🔥")

🔥

Click the arrow - I'll walk the program's path, line by line.

Code

1temp_str = input()
2temp = int(temp_str)
3if temp < 0:
4    print("Frost ❄️")
5elif temp < 15:
6    print("Cool 🧥")
7elif temp < 25:
8    print("Warm 🙂")
9else:
10    print("Heat 🔥")

Screen

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How an elif is built

Piece	How many	What it means
`if condition:`	exactly 1, at the start	the first sign
`elif condition:`	as many as you like	otherwise, maybe... - the next sign with a condition
`else:`	0 or 1, at the end	everything else - no condition

They all stand in line with each other, and each has its own indented lines. Python checks from the top and runs the lines of the first true condition - the rest is skipped.

A draw! 🎬

Remember the wrong apples from the last lesson? Click Next - we'll fix it with a third road.

Bajtek

That's not fair!😠

Code

ola = 6

kuba = 6

if ola > kuba:

print("Ola wins")

else:

print("Kuba wins")

🖥️ Screen

Kuba wins

❌ the wrong answer

A basketball match

Ola scored 6 baskets 🏀, and Kuba 6 too. The program with if-else says: "Kuba wins" - because 6 > 6 is False and else runs. But that's a draw!

Step 1 / 3

Who won the match? 🏀

Type Ola's 👧 points, then Kuba's 🧒 - Enter ⏎ after each number. Try two equal numbers too!

🏀1ola_str = input()

2ola = int(ola_str)

3kuba_str = input()

4kuba = int(kuba_str)

if ola > kuba

6print("Ola wins")

👧

elif kuba > ola

8print("Kuba wins")

🧒

elsein every other case

10print("A draw 🤝")

🤝

Click the arrow - I'll walk the program's path, line by line.

Code

1ola_str = input()
2ola = int(ola_str)
3kuba_str = input()
4kuba = int(kuba_str)
5if ola > kuba:
6    print("Ola wins")
7elif kuba > ola:
8    print("Kuba wins")
9else:
10    print("A draw 🤝")

Screen

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School marks

At school the points from a test are turned into a mark:

Points	Mark
90 and more	5
75 - 89	4
50 - 74	3
less than 50	2

In Python we write it starting from the highest limit:

The mark for 82 points

82 >= 90? No. 82 >= 75? Yes - mark 4, and the rest is skipped.

📝1points = 82

if points >= 90

3mark = 5

5️⃣

elif points >= 75

5mark = 4

4️⃣

elif points >= 50

7mark = 3

3️⃣

elsein every other case

9mark = 2

2️⃣

10print(mark)

Click the arrow - I'll walk the program's path, line by line.

Code

1points = 82
2if points >= 90:
3    mark = 5
4elif points >= 75:
5    mark = 4
6elif points >= 50:
7    mark = 3
8else:
9    mark = 2
10print(mark)

Screen

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The order matters 🎬

Click Next - one sign in the wrong place gives the wrong mark.

Bajtek

Code

points = 95

if points >= 50:

mark = 3

elif points >= 90:

mark = 5

🖥️ Screen

Kuba has 95 points

Kuba has 95 points in a test - that's a 5! But Kuba's program starts from the lowest limit: first points >= 50.

Step 1 / 3

The wrong order in action

The robot stops at the first green sign - and never reaches >= 90.

📝1points = 95

if points >= 50

3mark = 3

3️⃣

elif points >= 90

5mark = 5

5️⃣

elsein every other case

7mark = 2

2️⃣

8print(mark)

Click the arrow - I'll walk the program's path, line by line.

Code

1points = 95
2if points >= 50:
3    mark = 3
4elif points >= 90:
5    mark = 5
6else:
7    mark = 2
8print(mark)

Screen

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What will this program print?

n = 0
if n > 0:
    print("plus")
elif n < 0:
    print("minus")
else:
    print("zero")

What will this program print?

x = 20
if x > 5:
    print(1)
elif x > 10:
    print(2)
else:
    print(3)

How many times can elif appear?

Remember

elif condition: - otherwise, maybe... - the next sign with a condition.
The order: first if, then any number of elifs, at the end (maybe) else.
Python checks from the top and runs only the first true condition.
When the limits are inside each other, start from the highest one (or the lowest with <).
Three results (win, loss, draw) - a job for if, elif, else.

Now tasks with many roads! Remember the order of the signs.

Tasks from the video

We solve them together in the video - pause it and try first on your own.

1The sign of a number 2A draw 3The thermometer 4A test mark 5Pool prices 6The comparison sign 7T-shirt size 8Time of day

Practice tasks

Try to solve them without the video. Stuck? Every task has hints and an editorial.

9How many digits?10A medal 11Discounts 12Day of the week