Include `math.sign`

[oscarbenjamin]

@Lucas_Malor

But since we only need to check if x > 0, x == 0 and x < 0 – and maybe if the input x is a NaN, – is it really needed to convert the input to a float?

Take a look at my comment over here:

Typing custom integer class

In practice when it comes to numeric types you could never really just rely on duck-typing as a general approach. I’m sure it is the same in SageMath as in other libraries where for SymPy, NumPy etc every public function has to convert every potentially numeric input parameter to its own numeric types: def public_func(x): x = convert_to_known_types(x) # Now do stuff with x With or without static typing that is needed because you have to validate the inputs and the different numeric ty…

It just isn’t well defined to try to duck-type these things. There are many different numeric and non-numeric types in Python that implement operators like < and == in many different ways returning varying types and having varying semantics.

If you want well-defined predictable behaviour then you need a well-defined and predictable way of getting the inputs to known numeric types and __float__ is the math module’s way of doing that.