TL;DR:
Alsways use if variable is None

• if variable:
• if variable == None
• if variable is None

1. Using if variable:

This pattern checks the “truthiness” of variable. In Python, the following are considered False:

• Empty sequences and collections ('', (), [], {}, set())
• None
• False
• Zero of any numeric type (0, 0.0, etc.)

Example

items = [[], {}, set(), None, False, 0, 0.0]
for item in items:
    if not item:
        print(item)

Output:

Here, if not item: checks for all falsy values in the items list and prints them.

When to Use

Use if variable: when you want to verify that variable is “truthy” (i.e., not empty, not None, and not zero). It’s a concise and Pythonic way to perform general checks.

2. Using if variable == None

This approach checks if variable is equal to None using the equality operator ==.

Example

value = None

if value == None:
    print("Value is None.")
else:
    print("Value is not None.")

Output:

Why It’s Not Recommended

• Readability: if variable is None is clearer and more explicit.
• Correctness: The == operator can be overridden in custom classes, potentially leading to unexpected behavior.

3. Using if variable is None

The most Pythonic way to check for None is using the is operator, which checks for object identity.

Example

value = None

if value is None:
    print("Value is None.")
else:
    print("Value is not None.")

Output:

Advantages

• Clarity: Clearly indicates that you’re checking for the None object.
• Performance: Slightly faster as it doesn’t involve method calls.
• Safety: Not affected by overridden == methods in custom classes.

Best Practices

1. Use is for None Checks:

   • Prefer if variable is None or if variable is not None.
   • Avoid using == or != for None comparisons.

2. Use Truthiness for General Checks:

   • Use if variable: to verify that variable is “truthy.”
   • Use if not variable: to check if variable is “falsy.”

3. Be Clear and Explicit:

   • While concise code is valued, clarity should never be sacrificed. Choose the method that best conveys your intent.

Conclusion

Choosing the right if statement pattern enhances both the readability and reliability of your Python code. Use if variable: for general truthiness checks and if variable is None: when specifically checking for None. This approach helps prevent bugs and makes your code more maintainable.

Further Reading

• Python’s is vs == Operators
• PEP 8 — Style Guide for Python Code

References

• Python Documentation: Comparisons
• Real Python: Python If…Else

About the Author

Passionate Python developer and educator, dedicated to making programming accessible and enjoyable.

Comments

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Tags

Python, Programming, Conditional Statements, Best Practices

Categories

Programming Tutorials

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