Python Boolean Testing

def fun1():
    pass

def fun2():
    return False

def fun3():
    return True

print(fun1, fun2, fun3)

print(bool("<function fun1 at 0x0000024A75F95310>"), bool('<function fun2 at 0x0000024A75F95C10>'), bool('<function fun3 at 0x0000024A75F95700>'))

Thank you Cesar Aguilar. After print(fun1, fun2, fun3) we have the functions’ memory locations but return is string like print(bool("<function fun1 at 0x0000024A75F95310>"), bool('<function fun2 at 0x0000024A75F95C10>'), bool('<function fun3 at 0x0000024A75F95700>')) or depend on dunder __bool__ method for function class I do not now if function class has dunder __bool__ method or not.

If I do this:

print(bool(fun1()), bool(fun2()), bool(fun3()))

bool() returns the return value of function

@engmoh321 I’m not sure if I follow your question correctly, but let me try to break it down for you.

The bool() function takes whatever parameter you pass to it and tries to convert it into a Boolean value, i.e., either True or False, according to a few rules.

If you pass one of the built-in data types, such as a number, then most values will become truthy, while only one will usually be falsy, for example:

>>> # Integers are truthy except for zero
>>> bool(42), bool(-42), bool(0)
(True, True, False)

>>> # Floats are truthy except for zero
>>> bool(3.14), bool(-3.14), bool(0.0)
(True, True, False)

>>> # Functions are always truthy
>>> def foo():
...     pass
>>> bool(foo)
True

Objects such as strings or lists that have a length property are falsy only when their length is zero: (They define a special method .__len__(), which can be tested with the len() function.)

>>> # Strings are truthy except for the empty string
>>> bool("Hello"), bool("")
(True, False)

>>> # Collections are truthy except when they're empty
>>> bool(list()), bool(tuple()), bool(dict()), bool(set())
(False, False, False, False)
>>> bool([1]), bool((1,)), bool({1:1}), bool(set([1]))
(True, True, True, True)

Finally, your custom data types can define a special method .__bool__() to implement truth value testing:

class User:
    def __init__(self, is_admin):
        self.is_admin = is_admin

    def __bool__(self):
        return self.is_admin

user = User(is_admin=False)

if user:
    print("The admin can view private data")
else:
    print("An anonymous user can't view private data")

I hope this clears it up for you.

Thank you Bartosz Zaczyński. If I use function with return bool() function will return function return value:

def foo():
    return False
bool(foo())
#False

@engmoh321 Here’s what happens:

1. Python calls your function and evaluates its return value: foo()
2. It passes the return value False to the bool() function: bool(False)
3. Since False is already a Boolean, the call to bool() has no effect.
4. You get False.

def foo():
    return False
print(foo)
#<function foo at 0x000002020EAA53A0>

bool(foo)
#True

If print function name only without calling it return:

<function foo at 0x000002020EAA53A0>

This value (<function foo at 0x000002020EAA53A0>) truthy string.

@engmoh321 The bool() function converts its argument to a Boolean value and returns it, while the print() function converts its argument to a string representation and displays it on the screen.

Hello, at 3.25 why does the bool(func) return true and not false if func returns false?

@stehnacheric In this case, we’re calling bool() with the func function object as an argument rather than with the result of calling func(). Function objects, like many Python objects, evaluate to True. According to the documentation:

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. Here are most of the built-in objects considered false:

• constants defined to be false: None and False.
• zero of any numeric type: 0, 0.0, 0j, Decimal(0), Fraction(0, 1)
• empty sequences and collections: '', (), [], {}, set(), range(0)