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bool() in Python

  • Difficulty Level : Easy
  • Last Updated : 15 Sep, 2021

Python bool() function is used to return or convert a value to a Boolean value i.e., True or False, using the standard truth testing procedure. 

Syntax: bool([x])

bool() parameters

The bool() method in general takes only one parameter(here x), on which the standard truth testing procedure can be applied. If no parameter is passed, then by default it returns False. So, passing a parameter is optional. 

Return value from bool()

It can return one of the two values. 

  • It returns True if the parameter or value passed is True.
  • It returns False if the parameter or value passed is False.

 Here are a few cases, in which Python’s bool() method returns false. Except these all other values return True. 

  • If a False value is passed.
  • If None is passed.
  • If an empty sequence is passed, such as (), [], ”, etc
  • If Zero is passed in any numeric type, such as 0, 0.0 etc
  • If an empty mapping is passed, such as {}.
  • If Objects of Classes having __bool__() or __len()__ method, returning 0 or False

bool() function Python Example:

Example 1:

Python3




# Python program to illustrate
# built-in method bool()
 
# Returns False as x is False
x = False
print(bool(x))
 
# Returns True as x is True
x = True
print(bool(x))
 
# Returns False as x is not equal to y
x = 5
y = 10
print(bool(x == y))
 
# Returns False as x is None
x = None
print(bool(x))
 
# Returns False as x is an empty sequence
x = ()
print(bool(x))
 
# Returns False as x is an empty mapping
x = {}
print(bool(x))
 
# Returns False as x is 0
x = 0.0
print(bool(x))
 
# Returns True as x is a non empty string
x = 'GeeksforGeeks'
print(bool(x))

Output: 

False
True
False
False
False
False
False
True

Example 2:

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

Python3




# Python code to check whether a number
# is even or odd using bool()
 
def check(num):
    return(bool(num % 2 == 0))
 
# Driver Code
num = 8
if(check(num)):
    print("Even")
else:
    print("Odd")

Output: 

Even

bool() in Python input

Here we take input in boolean( True/ False) in boolean type with bool() function and check whether it is returned true or false.

Python3




user_input = bool(input("Are you hungry? True or false: "))
if user_input == "True":
    print(" You need to eat some foods ")
else:
    print("Let's go for walk")

Output:

Are you hungry? True or false: False
Let's go for walk


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