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bool() in Python - GeeksforGeeks

Last Updated : 21 Feb, 2025

In Python, bool() is a built-in function that is used to convert a value to a Boolean (i.e., True or False). The Boolean data type represents truth values and is a fundamental concept in programming, often used in conditional statements, loops and logical operations.

bool() function evaluates the truthness or falseness of a given value and returns either True or False. Understanding how bool() works is crucial for writing effective and efficient Python code.

Example:

x = bool(1)
print(x)
y = bool()
print(y)

bool([x])

• x: represents the value that we want to convert to a Boolean. If no argument is provided, bool() returns False by default.

The bool() function returns:

• True if the value x is considered "truth"
• False if the value x is considered "false."

In Python, certain values are considered "truth" or "false" based on their inherent properties. Here’s a breakdown:

False Values:

• False: The Boolean value False.
• None: The None keyword, which represents the absence of a value.
• 0: The integer zero.
• 0.0: The floating-point zero.
• "": An empty string.
• []: An empty list.
• (): An empty tuple.
• {}: An empty dictionary.
• set(): An empty set.
• range(0): An empty range.

Truth Values:

• Non-zero numbers (e.g., 1, -1, 3.14).
• Non-empty strings (e.g., "hello").
• Non-empty collections (e.g., [1, 2, 3], {"key": "value"}).
• Objects (e.g., instances of classes).

print(bool(True))    
print(bool(False))   
print(bool(0))       
print(bool(1))       
print(bool(-1))      
print(bool(0.0))     
print(bool(3.14))    
print(bool(""))      
print(bool("Hello")) 
print(bool([]))      
print(bool([1, 2]))  
print(bool({}))      
print(bool({"a": 1}))
print(bool(None))    

True
False
False
True
True
False
True
False
True
False
True
False
True
False

Explanation:

• bool(True) returns True because True is already a Boolean value.
• bool(False) returns False because False is already a Boolean value.
• bool(0) returns False because 0 is a false value.
• bool(1) returns True because 1 is a truth value.
• bool(-1) returns True because any non-zero number is truth.
• bool(0.0) returns False because 0.0 is a false value.
• bool(3.14) returns True because 3.14 is a non-zero number.
• bool("") returns False because an empty string is false.
• bool("Hello") returns True because a non-empty string is truth.
• bool([]) returns False because an empty list is false.
• bool([1, 2]) returns True because a non-empty list is truth.
• bool({}) returns False because an empty dictionary is false.
• bool({"a": 1}) returns True because a non-empty dictionary is truth.
• bool(None) returns False because None is a false value.

value = 10

if bool(value):
    print("The value is truth.")
else:
    print("The value is false.")

The value is truth.

Explanation:

• The bool(value) function is used to check if value is truth or false.
• Since value is 10, which is a non-zero number, bool(value) returns True.
• Therefore, the if block is executed, and the message "The value is truth." is printed.

class gfg:
    def __init__(self, value):
        self.value = value

    def __bool__(self):
        return bool(self.value)

obj1 = gfg(0)
obj2 = gfg(42)

print(bool(obj1))  
print(bool(obj2))  

Explanation:

• In this example, we define a custom class gfg with an __init__ method and a __bool__ method.
• The __bool__ method is a special method in Python that defines the truthiness of an object when bool() is called on it.
• When bool(obj1) is called, the __bool__ method of obj1 is invoked, which returns bool(self.value). Since self.value is 0, bool(obj1) returns False.
• Similarly, bool(obj2) returns True because self.value is 42, which is a non-zero number.

Here is a program to find out even and odd by the use of the bool() method. You may use other inputs and check out the results. 

def check_even(num):
    return bool(num % 2 == 0)

num = 8

if check_even(num):
    print("Even")
else:
    print("Odd")

Explanation:

1. num % 2 == 0 this checks if the number is divisible by 2.
2. bool(num % 2 == 0) converts the result into True (even) or False (odd).
3. conditional check if True, prints "Even" otherwise "Odd".

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