Python: None keyword in Python

None keyword in Python

Python None keyword in Python

1 Overview

📘 None in Python

In Python, None is a special constant that represents the absence of a value or a null value. It is often used to initialize variables or to indicate that a variable has not been assigned a value yet. None is an object of its own data type, NoneType.

2 What’s the difference between is and == in Python?

The == operator is for value equality. It’s used to know if two objects have the same value. The is operator is for reference equality. It’s used to know if two references refer (or point) to the same object, i.e if they’re identical. Two objects are identical if they have the same memory address. Two objects having equal values are not necessarily identical.

• In a few words:
  • Put simply: == determines if the values of two objects are equal, while is determines if they are the exact same object.
  • or even simpler: the is statement is syntactic sugar for id(a) == id(b).
  • The id() function is a built-in function in Python. It accepts a single parameter and is used to return the identity of an object.

3 None Keyword

• None is a special constant representing the absence of a value or a null value.
• It is commonly used as a placeholder to indicate that a variable should not have any value.

Example:

a = None
print(type(a))  # <class 'NoneType'>

4 Comparison with None

• There are several ways to compare if a variable is None:
  • The recommended and idiomatic way to check if a variable is None is using the is keyword.
  • Using == works in most cases but can lead to incorrect results in some specific advanced cases.

Example:

The is keyword works because Python stores a single instance of None in memory. Every variable equal to None points to the same memory location.

To check if a variable is not None, use a combination of is not:

None evaluates to False in a condition similar to False, empty strings '', or 0.

Example:

5 Returning None in Functions

None is commonly used in the context offunction returns to indicate absence of value. There are different ways to return None:

5.1 No return statement

• A function without a return statement implicitly returns None.
• Good choice when the function is only meant to perform an action (like printing or updating), and the caller (return) does not need to use the return value.

5.2 Only Return (without expression)

• Writing return without a value also returns None.
• Used to explicitly indicate the function should return early without any result.

5.3 Explicitly return None

• Explicitly returns None.
• Makes it clear the function intentionally returns None.
• Normally understood as not having any value.