I would like to write a generic function that takes an instance of any type that implements all real number operations (such as int, float, fractions.Fraction, or third-party types). I found the numbers.Real ABC which works great for enforcing the type at runtime with a isinstance(x, numbers.Real) check, and all built-in real number numeric types in Python are registered as a virtual subclass of it.

But I found out the hard way that while it works great for run-time checks, it doesn’t work well for type annotation purposes because all major type checkers ignore usages of abc.ABC.register. So how do I annotate my parameters which accepts any real numeric type then?

This post in a discussion suggests using the typing.SupportsInt protocol in favor of the numbers.Integral ABC, but in my case I need a replacement for numbers.Real. Also, it only checks if a class implements __int__, not if it supports all integral operations. And something like typing.SupportsReal doesn’t exist… Would I just have to define my own protocol that checks for the existence of all real number operation dunder methods (__add__, __sub__, __mul__, __div__, __truediv__, etc…)?