`operator` seems a slightly odd place for this. My naive expectation would be that `float(floatlike_obj)` should do what you want, but it seems that's not the case (too permissive of input types?). So then, what about an alternate constructor on the float object, `float.from_floatlike(obj)`? This could be implemented as effectively:
class float:
@classmethod
def from_floatlike(cls, obj):
return cls(PyFloat_FromDouble(PyFloat_AsDouble(obj)))
which would work to get an instance of any float subclass after a round-trip through a double. I have no idea whether that's actually useful, though :)