Is `is None` or `== None` the Right Way to Check for Null in Python?

Understanding the Distinction Between "is None" and "== None"

Many novice programmers grapple with the difference between "is None" and "== None" in Python. This article clarifies this distinction to enhance your coding proficiency.

"is None" vs. "== None"

In Python, variables of any type may be assigned the special value of None to represent an empty or undefined value. However, there are two distinct ways to compare a variable to None:

• "is None" performs an identity check, determining if the variable references the exact same None object in memory.
• "== None" performs an equality check, comparing the value of the variable to None. This means that even if the variable does not hold the exact None object, it will still return True if its value is equal to None.

Practical Implications

In most cases, using "is None" is preferred to "== None". This is because the latter may lead to unexpected behavior if custom comparison operators are defined for the class to which the variable belongs. As noted in the Python documentation:

"A class is free to implement comparison any way it chooses, and it can choose to make comparison against None mean something."

General Rule

While the practical difference is often minimal, it is considered best practice to refrain from using "== None" and instead default to "is None" in most situations. This eliminates potential confusion or errors that may arise from customized comparison operators.

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