I concur with Raymond. This expands the API too much. Not just the float API, but the API of all numeric classes, including third-party classes. And since the existence of additional method in third-party classes (e.g. NumPy classes) can't be guarantied, this couldn't help in the case of msg286441.

The less harmful way is making math.isfinite() and like supporting non-float numeric types. Always return False for integer types and fall back to the is_finite() method. But even this can be too expensive.