Python Built-In Constants: True, False, None, Ellipsis, and NotImplemented

This guide explains Built-In Constants: True, False, None, Ellipsis, and NotImplemented through a focused example and practical reasoning. No prior knowledge of this specific operation is required.

Understanding the Concept

True and False are Boolean constants; None represents the absence of a value; Ellipsis is the object written ...; and NotImplemented tells Python’s binary-operation dispatch that a particular operation is unsupported. These objects are not interchangeable.

When You Would Use This

A function can return None when no result has been found.

Step-by-Step Example

result = None
print(result is None)
print(True + 1)
print(Ellipsis is ...)
print(NotImplemented is None)

How the Example Works

The outputs are True, 2, True, and False. Although bool is a subclass of int, using Boolean values as numbers is usually less readable.

Example Output

True
2
True
False

Try It Yourself

Create a function that returns a name or None and check the result using is None.

Common Beginner Mistakes

Using NotImplemented as if it were NotImplementedError.
Treating None, False, 0 and an empty string as the same semantic state.
Using ... as though it automatically provides a real implementation of a function.

Key Takeaways

True and False are Boolean constants; None represents the absence of a value; Ellipsis is the object written ...; and NotImplemented tells Python’s binary-operation dispatch that a particular operation is unsupported.
The outputs are True, 2, True, and False.
Avoid this mistake: Using NotImplemented as if it were NotImplementedError.