The Boolean Type (bool) in Python

2.5. The Boolean Type (bool) in Python#

The boolean type (bool) is one of the most fundamental data types in Python. It represents logical truth values, meaning something that can be true or false.

2.5.1. Boolean Values#

There are only two possible values for the boolean type:

  • True: Represents truth.

  • False: Represents falsehood.

Important: Note that True and False begin with a capital letter. In Python, this makes a difference! true (with a lowercase ‘t’) is not recognized as a boolean value.

2.5.1.1. Basic Example:#

is_raining = True
has_sun = False

print(f"Is it raining? {is_raining}")
print(f"Is it sunny? {has_sun}")
print(f"Type of variable 'is_raining': {type(is_raining)}")

2.5.2. Comparison (Relational) Operators#

Comparison operators are used to compare two values and always return a boolean value (True or False). They form the basis for conditionals (if, elif, else).

Operator

Description

Example

Result

==

Equal to

5 == 5

True

!=

Not equal to

5 != 10

True

>

Greater than

10 > 5

True

<

Less than

5 < 10

True

>=

Greater than or equal to

10 >= 10

True

<=

Less than or equal to

5 <= 5

True

2.5.2.1. Usage Examples:#

print("\n--- Comparison Operators ---")
x = 10
y = 5
z = 10

print(f"x == z: {x == z}")   # True (10 is equal to 10)
print(f"x != y: {x != y}")   # True (10 is not equal to 5)
print(f"x > y: {x > y}")     # True (10 is greater than 5)
print(f"y < x: {y < x}")     # True (5 is less than 10)
print(f"x >= z: {x >= z}")   # True (10 is greater than or equal to 10)
print(f"y <= z: {y <= z}")   # True (5 is less than or equal to 10)

# Comparing strings (case-sensitive)
name1 = "Alice"
name2 = "alice"
print(f"'{name1}' == '{name2}': {name1 == name2}") # False

2.5.3. Logical (Boolean) Operators#

Logical operators combine boolean values or comparison results to form more complex expressions.

Operator

Description

Example

Result

and

Returns True if both conditions are True.

True and False

False

or

Returns True if at least one condition is True.

True or False

True

not

Inverts the boolean value (True becomes False, False becomes True).

not True

False

2.5.3.1. Usage Examples:#

print("\n--- Logical Operators ---")
age = 25
has_driver_license = True
has_passport = False

# Using 'and'
can_drive = (age >= 18) and has_driver_license
print(f"Can drive? (age >= 18 and has_driver_license): {can_drive}") # True and True -> True

# Using 'or'
can_travel = has_passport or (age >= 21) # Hypothetical travel condition
print(f"Can travel? (has_passport or age >= 21): {can_travel}") # False or True -> True

# Using 'not'
does_not_have_passport = not has_passport
print(f"Does not have passport? (not has_passport): {does_not_have_passport}") # not False -> True

# Combination of operators
complex_expression = (age > 30 and has_driver_license) or (not has_passport)
print(f"Complex expression: {complex_expression}") # (False and True) or True -> False or True -> True

2.5.4. Using Booleans in Conditionals (if/elif/else)#

Boolean values are the backbone of control flow structures.

print("\n--- Booleans in Conditionals ---")
is_day = True
temperature = 28

if is_day and temperature > 25:
    print("It's a hot and sunny day!")
elif is_day and temperature <= 25:
    print("It's a pleasant day.")
else:
    print("It's night or the day was not defined.")

# Example with user input
answer = input("Do you like Python? (yes/no): ").lower()

if answer == "yes":
    print("That's great! Python is very versatile.")
elif answer == "no":
    print("Maybe you'll change your mind over time :)")
else:
    print("I didn't understand your answer. Please type 'yes' or 'no'.")

2.5.5. “Truthy” and “Falsy” Values (Boolean Evaluation of Other Types)#

In Python, many data types can be evaluated in a boolean context (like in an if condition) even without explicitly being True or False.

  • “Falsy” values (evaluated as False):

    • False (obviously)

    • None

    • 0 (the integer zero)

    • 0.0 (the float zero)

    • Empty strings ("", '')

    • Empty lists ([])

    • Empty tuples (())

    • Empty dictionaries ({})

    • Empty sets (set())

  • “Truthy” values (evaluated as True):

    • Anything that is not “falsy”.

    • Examples: True, any non-zero number (1, -5, 3.14), any non-empty string ("Hello", " "), any non-empty list/tuple/dictionary/set.

2.5.5.1. “Truthy” and “Falsy” Examples:#

print("\n--- 'Truthy' and 'Falsy' Values ---")

if 0:
    print("0 is True") # Will not be printed
else:
    print("0 is False") # Will be printed

if 1:
    print("1 is True") # Will be printed

if "":
    print("Empty string is True") # Will not be printed
else:
    print("Empty string is False") # Will be printed

if "Hello":
    print("Non-empty string is True") # Will be printed

my_list = []
if my_list:
    print("Non-empty list is True") # Will not be printed
else:
    print("Empty list is False") # Will be printed

my_list.append(1)
if my_list:
    print("Non-empty list is True") # Will be printed
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