Python Boolean Values¶

In Python, Boolean values represent one of two states: True or False.

We frequently evaluate expressions to yield a Boolean value. This typically happens when using comparison operators, membership operators, or when generally evaluating the "truthiness" of data.

# Evaluating comparison operators
print(10 > 9)   # Returns True
print(10 == 9)  # Returns False
print(10 < 9)   # Returns False

Using Booleans in Conditions¶

Comparison operators returning Booleans are the foundation of conditional logic, such as if statements:

a = 200
b = 33

if b > a:
    print("b is greater than a")
else:
    print("b is not greater than a")

The `bool()` Function¶

You can use the built-in bool() function to evaluate any object or value. It will return either True or False based on Python's rules for "truthiness" and "falsiness."

print(bool("Hello"))  # Returns True
print(bool(15))       # Returns True

Truthy Values (Most Values are True)¶

Almost any value is evaluated to True if it contains some sort of content.

Strings: Any string is True, except for empty strings.
Numbers: Any number is True, except 0.
Collections: Any list, tuple, set, or dictionary is True, except for empty ones.

bool("abc")
bool(123)
bool(["apple", "cherry", "banana"])

Falsy Values¶

There are very few values that evaluate to False. They generally represent "empty" or "null" concepts:

The boolean False
The None object
The number 0
Empty sequences and collections: "", (), [], {}

bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})

Objects with Custom Lengths¶

Another scenario where an object evaluates to False is if you are dealing with a custom class that has a __len__() method configured to return 0 or False.

class MyClass:
    def __len__(self):
        return 0

my_obj = MyClass()
print(bool(my_obj))  # Returns False

Booleans as Return Values¶

Functions can be designed to return Boolean values, which is highly useful for writing clean, readable conditions.

def my_function():
    return True

print(my_function())

Here is a practical example of using a Boolean-returning function directly within a conditional statement:

def my_function():
    return True

if my_function():
    print("YES!")
else:
    print("NO!")

Note: Python also has several built-in functions that return Boolean values. A common example is the isinstance() function, which checks if an object is instance of a class or not.