Allow Quantity.__mul__ and .__truediv__ with Reals

[llucax]

From:

• Add Quantity types and update formulas to produce typed Samples frequenz-sdk-python#422 (comment)

@llucax

I think in general we should also provide __mul__ and __truediv__ with other: float: Power.from_watts(10) / 2 == Power.from_watts(5).

@shsms

Also from a performance point of view, this might be bad, especially if we also want to support division by multiple types, and we have to call isinstance 3 times to get to the right type. And then isinstance(v, float) will reject ints, but the typing system will accept ints, so have to have an explicit runtime type check for ints also.

@llucax

With numbers.Real we need only one:

    def __truediv__(self, other: Current | Voltage | float) -> Voltage | Current | Power:
        if isinstance(other, Current):
            return Voltage(self._base_value / other._base_value, exponent=0)
        if isinstance(other, Voltage):
            return Current(self._base_value / other._base_value, exponent=0)
        if isinstance(other, numbers.Real):  # Only 1 extra `isinstance()` for all reals (`int` and `float` and whatever user-defined type that inherits from `numbers.Real`)
            return type(self)(self._base_value / other, exponent=0)
        raise TypeError(
            f"unsupported operand type(s) for /: '{type(self)}' and '{type(other)}'"
        )

>>> import numbers
>>> isinstance(1, numbers.Real)
True
>>> isinstance(1.0, numbers.Real)
True

[llucax]

This was actually already done, but using float only. Not sure if we should update it to use numbers.Real.

[llucax]

isinstance(x, numbers.Real) is ~15x slower than checking for float only and checking for both int and float takes almost the same as checking only for float, so probably not the best option 😬

$ python -m timeit 'isinstance(1.0, float)'
10000000 loops, best of 5: 20.2 nsec per loop
$ python -m timeit 'isinstance(1.0, float) or isinstance(1, int)'
10000000 loops, best of 5: 23.8 nsec per loop
$ python -m timeit -s 'import numbers' 'isinstance(1.0, numbers.Real)'
1000000 loops, best of 5: 314 nsec per loop

[Marenz]

We can wait until someone needs it..

[llucax]

You can always get around this by using power.as_watts() / 2, it is just a convenience issue. But yeah, I think it is a pretty niche case to want to use an int, if it is a literal you can just add a .0 and if not you can convert it, but it should be pretty rare.

[llucax]

So I will close this discussion, anyone can reopen it if they think it is still "a thing".