Which answer is correct?

Use `if x is None:`. The `is` operator checks identity, and there is exactly one `None` object in Python.

— pythonic_dev

Use `if x == None:`. Equality comparison works and is more intuitive.

— simple_approach

Use `if not x:`. This catches None, False, 0, and empty collections.

— falsy_fan

Use `if x is not None:` for the inverse check. Never use `if x != None:`.

— pep8_follower