04-booleans

04 · Booleans & Comparison

Part 1 — Fundamentals · Estimated time: 20–30 min · Prerequisite: 02 · Data Types & Numbers

A boolean is a value that is either True or False. Booleans are how programs answer yes/no questions — and answering questions is how programs make decisions (which you'll do for real in the next lesson, Conditionals). Here we learn how to produce True/False values by comparing and combining things.

What you'll learn

• The two boolean values: True and False
• Comparison operators: ==, !=, <, >, <=, >=
• Logical operators: and, or, not
• "Truthiness" — which everyday values count as True or False
• The classic = vs == mix-up

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1. True and False

is_open = True
is_raining = False
print(type(is_open))   # <class 'bool'>

Comparisons produce booleans — that's where they usually come from:

print(10 > 3)     # True
print(2 == 5)     # False

▶️ Run it: python examples/01_true_and_false.py

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2. Comparison operators

Operator	Means	Example	Result
==	equal to	5 == 5	True
!=	not equal to	5 != 3	True
>	greater than	5 > 8	False
<	less than	5 < 8	True
>=	greater or equal	5 >= 5	True
<=	less or equal	4 <= 3	False

⚠️ = vs ==: a single = assigns a value (x = 5). A double == compares (x == 5 asks "is x equal to 5?"). Mixing them up is the #1 beginner bug.

▶️ Run it: python examples/02_comparison_operators.py

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3. Logical operators: and / or / not

Combine yes/no answers into a bigger answer.

print(True and False)   # False  -> and needs BOTH to be True
print(True or False)    # True   -> or needs only ONE to be True
print(not True)         # False  -> not flips it

age = 25
print(age >= 18 and age < 65)   # True  -> "an adult under 65"

▶️ Run it: python examples/03_logical_operators.py

💡 Try it yourself: write a comparison that is True only when a number n is outside the range 0–100 (less than 0 or more than 100).

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4. Truthiness

Python can treat almost any value as a yes/no answer. These count as falsy (act like False): 0, 0.0, "" (empty string), [] (empty list), and None. Everything else is truthy. bool(value) shows you which.

print(bool(0))        # False
print(bool(""))       # False
print(bool("hi"))     # True
print(bool([]))       # False
print(bool([1, 2]))   # True

This is why you'll later see if name: meaning "if name isn't empty."

▶️ Run it: python examples/04_truthiness.py

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Common mistakes

Mistake	What happens	Fix
if x = 5:	SyntaxError	Use == to compare: x == 5.
True vs "True"	the string "True" is just text (and always truthy)	Use the real keyword True, no quotes.
1 < x < 10 confusion	actually this works in Python!	Chained comparisons are allowed and read naturally.
not x == y ambiguity	works, but clearer as x != y	Prefer != for "not equal".

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Recap / cheat-sheet

True, False              # the two boolean values
a == b   a != b          # equal / not equal
a < b    a > b           # less / greater
a <= b   a >= b          # less-or-equal / greater-or-equal
a and b                  # both must be True
a or b                   # at least one True
not a                    # flip it
bool(value)              # truthy or falsy?
# falsy: 0, 0.0, "", [], None   (everything else is truthy)

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Exercises

Run a file with python exercises/<file>.py, then compare with the matching file in solutions/.

1. exercises/01_can_vote.py — turn an age into a True/False "can vote?" answer.
2. exercises/02_in_range.py — check whether a number sits inside a range.
3. exercises/03_truthy_or_falsy.py — predict and print the truthiness of several values.

Try each yourself before opening the solution.

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Next → 05 · Operators, Expressions & Statements (coming soon)