15. What is the output produced by following code ?
a, b = bool(®), bool(0.0)
c, d = str(©), str(0.0)
print (len(a), len(b))
print (len(c), len(d))
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Python bool() function returns Boolean value for an object. The bool class has only two instances – True and False. This class can’t be extended.
Table of Contents
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1 Python bool()
2 Python bool() example
3 Python bool() with strings
4 Python bool() with numbers
5 Python bool() function with collections and sequences
6 Python bool() function with custom object
Python bool()
Python bool() function uses standard truth testing rules to convert the specified argument object to Boolean value.
Some of the rules used to return Boolean value are:
Any object Boolean value is considered true if it’s not implementing __bool__() function and __len__() functions.
If the object doesn’t define __bool__() function but defines __len__() function, then __len__() function is used to get the boolean value of object. If __len__() returns 0, then bool() function will return False otherwise True.
Boolean value will be False for None and False constants.
Boolean value will be False for zero value numbers such as 0, 0.0, 0j, Decimal(0), and Fraction(0, 1).
Boolean value will be False for empty sequences (tuple, dict) and collections, such as ”, (), [], {} etc.
Python bool() example
Let’s look at some simple examples of bool() with bool instances and None.
x = True b = bool(x) print(type(x))
# <class 'bool'>
print(type(b))
# <class 'bool'>
print(b)
# True
x = False b = bool(x) print(b)
# False
x = None b = bool(x) print(type(x))
# <class 'NoneType'>
print(type(b))
# <class 'bool'>
print(b)
# False
The output is self-explained and provided in the comments.
Python bool() with strings
# string examples
x =
'True'
b = bool(x)
(
type
(x))
# <class 'str'>
(
type
(b))
# <class 'bool'>
(b)
# True
x =
'False'
b = bool(x)
(b)
# True because len() is used
x =
''
(bool(x))
# False, len() returns 0