Python — Booleans

What are Booleans?

Booleans represent one of two values: True or False:

is_active = True
is_deleted = False

Note the capital T and F — Python booleans are capitalized.

Creating Booleans

# Direct values
a = True
b = False

# From comparisons
x = 5 > 3      # True
y = 10 == 5    # False
z = 5 != 3     # True

# From function returns
is_even = lambda n: n % 2 == 0
is_even(4)     # True

Comparison Operators

These return booleans:

Operator	Meaning	Example
==	Equal	5 == 5 → True
!=	Not equal	5 != 3 → True
>	Greater than	5 > 3 → True
<	Less than	5 < 3 → False
>=	Greater or equal	5 >= 5 → True
<=	Less or equal	5 <= 3 → False

x = 10
print(x > 5)    # True
print(x == 10)  # True
print(x != 5)   # True

Logical Operators

Operator	Meaning	Example
and	Both must be True	True and False → False
or	At least one True	True or False → True
not	Flips the value	not True → False

and

age = 25
has_id = True

if age >= 21 and has_id:
    print("Entry allowed")

or

is_weekend = False
is_holiday = True

if is_weekend or is_holiday:
    print("Day off!")

not

is_logged_in = False

if not is_logged_in:
    print("Please log in")

Truthiness and Falsiness

Python treats certain values as True or False:

Falsy Values

False
0
0.0
0j          # complex zero
""          # empty string
[]          # empty list
()          # empty tuple
{}          # empty dict
set()       # empty set
None

Truthy Values

True
1           # any non-zero number
-1
"hello"     # any non-empty string
[1, 2]      # non-empty list
{"a": 1}    # non-empty dict

Using Truthiness

# Check if list has items
items = [1, 2, 3]
if items:
    print("List is not empty")

# Check if string is not empty
name = ""
if not name:
    print("Name is empty")

# Check if number is non-zero
count = 0
if count:
    print("Count is non-zero")

bool() Function

Convert any value to boolean:

bool(0)          # False
bool("")         # False
bool(None)       # False
bool([])         # False

bool(1)          # True
bool("hello")    # True
bool([1, 2])     # True
bool({"a": 1})   # True

Short-Circuit Evaluation

Python stops evaluating as soon as the result is determined:

# and — returns first falsy value
result = "" and "hello"  # "" (empty string is falsy)
result = "hi" and "hello"  # "hello"

# or — returns first truthy value
result = "" or "default"  # "default"
result = "hello" or "world"  # "hello"

# Practical use: default values
name = user_name or "Anonymous"

Ternary Conditional

# condition_if_true if condition else condition_if_false
status = "adult" if age >= 18 else "minor"

# Nested ternary (avoid for readability)
grade = "A" if score >= 90 else "B" if score >= 80 else "C"

Common Patterns

# Check membership
if "apple" in fruits:
    print("Found apple")

# Guard clauses
if not user:
    return redirect("/login")

# Boolean flag
is_running = True
while is_running:
    # game loop
    if should_quit:
        is_running = False

# Toggle
lights_on = not lights_on

Best Practices

• Use is for None comparisons: if x is None
• Use == for value comparisons: if x == 5
• Don't compare booleans to True/False explicitly
  • Bad: if is_active == True
  • Good: if is_active
• Use truthiness for checking emptiness: if items: not if len(items) > 0
• Use not for negation: if not items:

Mini Practice

1. Create variables and compare them with all comparison operators
2. Write a condition using and, or, and not
3. Test truthiness of different values with bool()
4. Use short-circuit evaluation to set default values
5. Write a ternary expression to classify a number

Up Next

Next: Strings →