How to "test" NoneType in python?

Question

I have a method that sometimes returns a NoneType value. So how can I question a variable that is a NoneType? I need to use if method, for example

if not new:     new = '#' 

I know that is the wrong way and I hope you understand what I meant.

Answer 1

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.

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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.