Booleans and None

Big idea

A boolean (bool) is either True or False — the answer to a yes/no question. None means "no value at all".

Booleans

is_raining = True
has_umbrella = False

Capital T, capital F, no quotes. You'll rarely type them directly, though — they usually come from a comparison:

age = 15
print(age >= 13)
print(age >= 18)
print(type(age >= 18))

output
True
False
<class 'bool'>

Every if and every loop you'll write in this course runs on booleans.

Truthy and falsy

Python can treat any value as true or false. bool(...) shows you which. The rule: empty or zero is False; everything else is True.

print(bool(0))
print(bool(42))
print(bool(""))
print(bool("no"))
print(bool(None))

False
True
False
True
False

"no" is True — it's a non-empty string. Python doesn't read the word.

Watch it

None

None is Python's "nothing here". It's used for "not set yet" or "no answer":

winner = None          # no winner yet

To check for it, use is:

winner = None
print(winner is None)
winner = "Grace"
print(winner is None)

output
True
False

It's its own type — type(None) is NoneType — and it isn't the same as 0, "", or False, even though all of them are falsy.

ready = true
print(ready)

output
True

Think of it like

A light switch: True is on, False is off. None is a switch that hasn't been installed yet.

Key terms

• Boolean (bool) — True or False.
• Truthy / falsy — Whether a value counts as true or false; empty and zero are falsy.
• None — The value meaning "nothing".