Python Basics — Booleans & None

Booleans & None

Booleans and None are two of Python’s simplest but most important data types. Booleans represent truth values (True or False), while None represents the absence of a value.

Boolean Type (bool)

A boolean can only have two values: True or False.

is_active = True
is_deleted = False

print(type(is_active))  # <class 'bool'>
print(type(is_deleted))  # <class 'bool'>

Important: True and False must be capitalized. true or false will cause a NameError.

Boolean Operations

Python supports three boolean operators: and, or, and not.

a = True
b = False

print(a and b)   # False — both must be True
print(a or b)    # True — at least one must be True
print(not a)     # False — reverses the value
print(not b)     # True

Truth Tables

and — returns True only if both are True:

A	B	A and B
True	True	True
True	False	False
False	True	False
False	False	False

or — returns True if at least one is True:

A	B	A or B
True	True	True
True	False	True
False	True	True
False	False	False

not — reverses the value:

A	not A
True	False
False	True

Comparison Operators Return Booleans

print(5 > 3)      # True
print(10 == 10)    # True
print(7 != 7)      # False
print(3 >= 5)      # False
print("a" < "b")   # True (lexicographic comparison)

Truthy and Falsy Values

In Python, every value has a boolean equivalent. When used in a condition, some values are treated as False (falsy) and everything else is treated as True (truthy).

Falsy Values (evaluate to False)

Value	Type	Example
False	bool	bool(False) → False
0	int	bool(0) → False
0.0	float	bool(0.0) → False
0j	complex	bool(0j) → False
""	str (empty)	bool("") → False
[]	list (empty)	bool([]) → False
()	tuple (empty)	bool(()) → False
{}	dict (empty)	bool({}) → False
set()	set (empty)	bool(set()) → False
None	NoneType	bool(None) → False

Truthy Values (evaluate to True)

Everything that is NOT in the falsy list is truthy:

print(bool(1))         # True
print(bool(-1))        # True (any non-zero number)
print(bool("hello"))   # True (any non-empty string)
print(bool([1, 2]))    # True (any non-empty list)
print(bool(" "))       # True (space is not empty!)

Using Truthiness in Conditions

name = "Alice"
if name:  # Truthy — non-empty string
    print(f"Hello, {name}!")

items = []
if not items:  # Falsy — empty list
    print("Your cart is empty.")

Output:

Hello, Alice!
Your cart is empty.

The bool() Function

Convert any value to a boolean:

print(bool(42))       # True
print(bool(0))        # False
print(bool("hello"))  # True
print(bool(""))       # False
print(bool(None))     # False
print(bool([1]))      # True
print(bool([]))       # False

Booleans Are Integers

In Python, True is actually 1 and False is 0:

print(True + True)    # 2
print(True + False)   # 1
print(True * 10)      # 10
print(False * 10)     # 0

print(isinstance(True, int))   # True — bool is a subclass of int

This is useful for counting True values:

results = [True, False, True, True, False]
print(sum(results))  # 3 (counts True values)

The None Type

None represents the absence of a value. It’s Python’s version of “null” or “nothing.”

result = None
print(result)         # None
print(type(result))   # <class 'NoneType'>

Common Uses of None

# 1. Default variable value
user = None  # Will be set later

# 2. Function that doesn't return anything
def greet(name):
    print(f"Hello, {name}!")

result = greet("Alice")  # Hello, Alice!
print(result)            # None

# 3. Default parameter value
def find_user(user_id, database=None):
    if database is None:
        database = get_default_db()
    # ...

Checking for None

Always use is (not ==) to check for None:

x = None

# ✅ Correct — use "is"
if x is None:
    print("x has no value")

# ✅ Also correct — "is not"
if x is not None:
    print("x has a value")

# ❌ Works but not recommended
if x == None:
    print("This works but is not Pythonic")

Why is instead of ==? The is operator checks identity (same object in memory), which is exactly what we want for None. The == operator checks equality, which can be overridden by custom classes and produce unexpected results.

None vs False vs 0 vs “”

These are all falsy, but they are different values:

print(None == False)   # False
print(None == 0)       # False
print(None == "")      # False
print(False == 0)      # True (bool is subclass of int)

print(None is None)    # True (there's only one None)
print(False is False)  # True

Common Mistakes

Mistake	Example	Fix
Using == None	if x == None:	Use if x is None:
Lowercase boolean	true, false	Use True, False
Confusing None with ""	They’re different types	Check type if unsure
Assuming 0 means None	0 is None → False	They are different values

Summary

• Booleans have two values: True and False
• Use and, or, not for boolean operations
• Every Python value has a truthy or falsy equivalent
• Falsy values: False, 0, 0.0, "", [], (), {}, set(), None
• None represents the absence of a value (like null in other languages)
• Always use is None and is not None instead of == None
• Booleans are integers: True is 1, False is 0

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