Things That Are Falsy In Python

Python has a neat and simple truthy and falsy concept. This can make your programs more readable, easier to maintain and avoid logical errors. In general, truthiness in Python is about values that are not zero or non empty.

What is truthy and falsy values?

Truthy values are values that are considered to evaluate to True in a boolean context. In a similar way Falsy values are values that are considered to be False in a boolean context.

For example, the value 0 in Python is considered Falsy while 1 is considered Truthy.

In [1]: 0 == True
Out[1]: False

In [2]: 1 == True
Out[2]: True

All other numbers are evaluate to a Truthy value.

Truth value testing

Python documentation clearly states that we can distinguish the Truthy and Falsy values in 4 main categories.

1. Objects
2. Constants
3. Zero of any numeric built in type
4. empty collections or sequences.

Objects

Objects evaluate to True except if they define either the __bool__() or the __len__() method. Therefore, if you want your custom objects to evaluate to anything else other that True you can overwrite these two methods based on your business logic.

class MyClass:
   x = 1

my_object = MyClass()

if my_object:
    print('True')
else:
    print('False')

# result
True

After overwriting the __len__() method we can see that the result of the if statement is different.

class MyClass:
    x = 1
    def __len__(self):
        return 0

my_object = MyClass()


if my_object:
    print('True')
else:
    print('False')

# result
False

Constants

If a constant is defined as either None or False will evaluate to a Falsy value.

Numeric Types

All the 0 numeric types such as int, float, complex, Decimal and Fraction are evaluate to a Falsy value. For example all the values below are all false.

• 0, 0.0, 0j, Decimal(0), Fraction(0, 1)

Empty collections or sequences

All the built in empty sequences or collections are evaluate to a False value.

For example, '', (), [], {}, set(), range(0) are all false.

Summary

• Truthy values are values that areTrue in a boolean context.
• Falsy values are values are False in a boolean context.
• Python documentation states that there are 4 main categories of Falsy and Truthy items.
• If used correctly they can improve the readability and maintainability of your codebase.