Truth Value Testing in Python

December 26, 2020

Truth Value Testing

We can use any way to check the truth value of an object . By using ‘If’ statement or ‘While’ statement the checking can be done.

By default, an object is considered true unless its class defines either a __bool__() method that returns False or a __len__ method that returns zero, when called with the object.

Example :
  • x=1
    • bool(x)=True
  • x=1
    • if(x==1):
      • print(‘True’)
Truth Value Testing in Python

Truth Value Testing :

  • The truth value 0 is equivalent to False and 1 is same as True. 
  • When a variable contains different values like 0, 0.0, Fraction(0, 1), Decimal(0), then it signifies the False Value.
  • Truth value of an empty sequence is False. 
implementation of truth value testing in python

Code :

#python Program 
#The class Prep has no __bool__ method, so default value of it is True
class Prep: 
   def __init__(self):
      print(‘This is class Prep’)
        
p_obj = Prep()

if p_obj:
   print(‘It is True’)
else:
   print(‘It is False’)

#The class Insta has __bool__ method, which is returning false value    
class Insta: 
   def __init__(self):
      print(‘This is class Insta’)
        
   def __bool__(self):
      return False
I_obj = Insta()
if I_obj:
   print(‘It is True’)
else:
   print(‘It is False’)
Tupl = (4,7, 8,41) # Some elements are available, so it returns True
if Tupl:
   print(‘Not Empty’)
else:
   print(‘Empty’)
lis = [] # No element is available, so it returns False
if lis:
   print(‘Not Empty’)
else:
   print(‘Empty’)
    
Output:

This is class Prep
It is True
This is class Insta
It is False
Not Empty
Empty