How to "test" NoneType in python? How to "test" NoneType in python? python python

How to "test" NoneType in python?

So how can I question a variable that is a NoneType?

Use is operator, like this

if variable is None:

Why this works?

Since None is the sole singleton object of NoneType in Python, we can use is operator to check if a variable has None in it or not.

Quoting from is docs,

The operators is and is not test for object identity: x is y is true if and only if x and y are the same object. x is not y yields the inverse truth value.

Since there can be only one instance of None, is would be the preferred way to check None.

Hear it from the horse's mouth

Quoting Python's Coding Style Guidelines - PEP-008 (jointly defined by Guido himself),

Comparisons to singletons like None should always be done with is or is not, never the equality operators.

if variable is None:   ...

if variable is not None:   ...

It can also be done with isinstance as per Alex Hall's answer :

>>> NoneType = type(None)>>> x = None>>> type(x) == NoneTypeTrue>>> isinstance(x, NoneType)True

isinstance is also intuitive but there is the complication that it requires the line

NoneType = type(None)

which isn't needed for types like int and float.