Bool() Function In Python

Function Name:

bool(object)

 

Function Overview:

  • The bool() function converts any object into a Boolean value.
  • The Boolean value returned is either True or False.

 

When an object evaluates to False in Python?

  • If the object has a value None, bool() function will return false

  • If the object has a value False,  bool() function will return false
  • If the value of the object is zero bool() will return false. Zero could be from any numeric type like int, floating point, complex type or a user defined type.
  • Empty sequences such as empty lists and empty mappings like empty dictionaries.
  • If the object belongs to a user defined type and the __bool__() method defined for such object returns False
  • If the object belongs to a user defined type and the __len__() method defined for such object returns zero

When an object evaluates to True Python?

When all of the above mentioned False criteria fail, the bool() function will return True.

 

Examples:

Example for python bool() function:

x           = 65

y           = 0

z           = None

listObject  = [1, 1, 2, 3, 5, 8]

 

print(bool(x))

print(bool(y))

print(bool(z))

print(bool(listObject))

Example output from python bool() function:

True

False

False

True

Example for objects evaluating to Boolean values:

# False by default

visibility = False;

 

if (visibility):

    print("Yes...visibile")

else:

    print("No...Not visibile")

 

 

# None values evaluate to false

initState = None

if(initState):

    print("Yes...Initialized")

else:

    print("No...Not initialized")

 

#Custom int class

class SpecialInt:

    myVal=0

   

    def __init__(self, aVal_in):

        self.myVal = aVal_in

       

    def __bool__(self):

        if(self.myVal):

            return True

        else:

            return False

 

SpecialIntObject = SpecialInt(1)

if(SpecialIntObject):

    print("SpecialIntObject evaluates to true")

else:

    print("SpecialIntObject evaluates to false")

   

   

listObject = [1,2,3]

emptyList  = []

 

if(listObject):

    print("List with elements evaluate to true")

   

if(emptyList):

    print("Strange")

else:

    print("Empty list evaluate to false")   

 

Example output for objects evaluating to Boolean values:

No...Not visibile

No...Not initialized

SpecialIntObject evaluates to true

List with elements evaluate to true

Empty list evaluate to false

 


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