None Python error/bug?

Question

In Python you have the None singleton, which acts pretty oddly in certain circumstances:

>>> a = None
>>> type(a)


        

Answer 1

None is the just a value of types.NoneType, it's not a type.

And the error is clear enough:

TypeError: isinstance() arg 2 must be a class, type, or tuple of classes and types

From the docs:

None is the sole value of types.NoneType. None is frequently used to represent the absence of a value, as when default arguments are not passed to a function.

You can use types.NoneType

>>> from types import NoneType
>>> isinstance(None, NoneType)
True

is operator also works fine:

>>> a = None
>>> a is None
True