Lesson 25

and, or, not - joining conditions

After this lesson: You'll join several conditions into one: all at once (and), at least one (or) or the other way round (not).

Video

The video for this lesson is coming soon.

Explanation

Sometimes one condition isn't enough. You can get on the ride when you're 120 cm and have a ticket. Ice cream is free when it's your birthday or it's Sunday. To join conditions Python has three little words: and, or and not. Today you'll see them as... electricity! ⚡

A door with two locks 🎬

Click Next - and is two locks that must both be open.

Bajtek

🔒🔒🚪💎

Bajtek's treasury

Bajtek hides treasure 💎 behind a door with two locks. Each lock opens with a different key: a red one 🔴 and a blue one 🔵.

Step 1 / 4

Lab: and ⚡

Click the switches. With and they stand one after another - current has to pass through both.

💡 I get on: False

I'm 120 cm	I have a ticket	I'm 120 cm and I have a ticket
True	True	True 💡
True	False	False
False	True	False
False	False	False

and: the switches stand one after another. Click them - the bulb lights only when ALL of them are on.

The ride: height and ticket

Both conditions are true - current flows through both switches and the bulb shines.

🔋 ─ ⏻ ─ 💡

Click the arrow - you'll see the condition as a circuit with switches and a bulb.

Code

1height = 130
2ticket = True
3if height >= 120 and ticket:
4    print("Get on!")
5else:
6    print("Not this time")

Screen

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No ticket

One switch is open - the current won't pass, even though the height is fine.

🔋 ─ ⏻ ─ 💡

Click the arrow - you'll see the condition as a circuit with switches and a bulb.

Code

1height = 130
2ticket = False
3if height >= 120 and ticket:
4    print("Get on!")
5else:
6    print("Not this time")

Screen

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Free ice cream 🎬

Click Next - or is two roads to the same prize.

Bajtek

🎂or📅Sunday➡️🍦

A deal at the ice cream shop

The ice cream shop has a sign: free ice cream if it's your birthday or it's Sunday 🍦. One of the two is enough!

Step 1 / 4

Lab: or ⚡

With or the switches stand side by side - the current has two roads. One is enough!

💡 free ice cream: True

it's my birthday	it's Sunday	it's my birthday or it's Sunday
True	True	True 💡
True	False	True 💡
False	True	True 💡
False	False	False

or: the switches stand side by side. Click them - ONE switch on is enough for the bulb to shine.

Free ice cream in Python

Day 3 is Wednesday, but it's a birthday - one road is enough.

🔋 ─ ⏻ ─ 💡

Click the arrow - you'll see the condition as a circuit with switches and a bulb.

Code

1birthday = True
2day = 3
3if birthday or day == 7:
4    print("Free ice cream! 🍦")
5else:
6    print("Ice cream for 5 zloty")

Screen

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not - the other way round

The third little word, not, flips the answer: not True is False, and not False is True. It's handy when something should happen when a condition is not met:

if not raining:
    print("Let's go for a walk")

We read it: if it's not raining - let's go for a walk.

Lab: not ⚡

not is a switch that works the other way round. Click it and see!

💡 a walk: False

raining	not raining
True	False
False	True 💡

not: the switch works the other way round. Click it - when the condition is True the bulb goes out, and when it's False it shines.

A walk when it isn't raining

raining is False, and not turns it into True - the bulb shines.

🔋 ─ ⏻ ─ 💡

Click the arrow - you'll see the condition as a circuit with switches and a bulb.

Code

1raining = False
2if not raining:
3    print("Let's go for a walk 🌳")
4else:
5    print("We stay at home")

Screen

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A number in a range

A very common question: is a number between 10 and 20? That's two conditions at once - so and:

if n >= 10 and n <= 20:

Python also knows a shorter way, like in maths: 10 <= n <= 20. Both mean the same - pick the one you understand better.

Question	Condition
n from 10 to 20	`n >= 10 and n <= 20`
n outside the range 0..100	`n < 0 or n > 100`
Saturday or Sunday	`day == 6 or day == 7`

Are you a teenager? 🧑

A teenager is 13 to 19 years old. Type an age 🎂 and press Enter ⏎ - the current passes only through two closed switches.

🔋 ─ ⏻ ─ 💡

Click the arrow - you'll see the condition as a circuit with switches and a bulb.

Code

1age_str = input()
2age = int(age_str)
3if age >= 13 and age <= 19:
4    print("A teenager!")
5else:
6    print("Not a teenager")

Screen

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The weekend? 📅

Type the number of a day of the week 📅 (1 - Monday, 7 - Sunday) and press Enter ⏎.

🔋 ─ ⏻ ─ 💡

Click the arrow - you'll see the condition as a circuit with switches and a bulb.

Code

1day_str = input()
2day = int(day_str)
3if day == 6 or day == 7:
4    print("The weekend! 🎉")
5else:
6    print("School 🎒")

Screen

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A trap: or with a bare number

Kuba writes if day == 6 or 7: - and the program always says The weekend! Why? Python reads it as (day == 6) or 7, and the bare number 7 (not zero) counts as True. Each side of or must be a whole question: day == 6 or day == 7.

What will this program print?

n = 15
print(n > 10 and n < 20)

What will this program print?

n = 5
print(n < 0 or n > 100)

What does print(not 3 > 1) print?

print(not 3 > 1)

Which condition checks whether n is between 1 and 9?

Remember

and - true when all the parts are true (switches one after another).
or - true when at least one part is true (switches side by side).
not - flips: not True is False, not False is True.
A range: n >= 10 and n <= 20 or 10 <= n <= 20.
Each side of or / and must be a whole question: day == 6 or day == 7.

On to the tasks! First think: do you need all the conditions (and), or is one enough (or)?

Tasks from the video

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

1From 10 to 20 2A ride for older kids 3The weekend 4Out of range 5Both positive 6At least one even 7A walk 8Can a triangle be built?

Practice tasks

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

9A teenager 10School hours 11A lucky number 12Exactly one positive