CPAlgorithms: use identity operators instead of equality for python enums

As recommended in PEP-8

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

Also, beware of writing if x when you really mean if x is not None – e.g. when testing whether a variable or argument that defaults to None was set to some other value. The other value might have a type (such as a container) that could be false in a boolean context!

When comparing Enum members, identity (is) comparisons are preferred over equality (==) comparisons.