Perform operations on values with class attributes

Question

Let's say I've made a simple class

class mercury:

    class orbial_characteristics:
        apehilion = 69816900
        perihilion = 46001200
        semi_major_axis = 57909050
        eccentricity = 0.205630
        orbital_period = 87.9691*86400
        orbital_speed = 47.362*1e3

Now, the values given here are in SI units, the value of apehilion for example, is in km. I want to make another class that can convert the value to a given unit, let's say astronomical unit. One method is to pass the value of apehilion directly to that class

change_to_AU(value_of_apehilion)

Which is relatively easy to do. However, what I'm looking for is in the lines of python core operations. Something like this

merc_apehilion_km = mercury.orbital_characteristics.apehilion
merc_apehilion_au = merc_apehilion_km.change_to_AU()

I have recently started working on classes, by reading answers here and web tutorials but I do not get how such an operation can be performed. I even try reading the core files from numpy and pandas as these two libraries that I use most have a number of things that use this notation.

Answer 1

Edit:

A little research led me to this stack overflow page. Take a look at the libraries mentioned in it, make sure they are actively maintained, and consider using them over doing what I demonstrate below

End of Edit

Creating custom methods like this would involve you creating a custom Object for your SI unit values. Here is an example:

class SIUnit:
    def __init__(self, value):
        self.value = value

    def __str__(self):
        return self.value

    def to_astronimical_units(self):
        Calculations which convert apehilion to AU go here

        return result

class mercury:

    class orbial_characteristics:
        apehilion = SIUnit(69816900)
        perihilion = SIUnit(46001200)
        semi_major_axis = SIUnit(57909050)
        eccentricity = SIUnit(0.205630)
        orbital_period = SIUnit(87.9691*86400)
        orbital_speed = SIUnit(47.362*1e3)

Keep in mind that the to_astronomical_units method would exist for all SI units you use, not just distance so you may want to create a base SIUnit class then have a subclass for each SI Unit, e.g:

class SIUnit:
    def __init__(self, value):
        self.value = value

    def __str__(self):
        return self.value

class Kilometer(SIUnit):
    def to_au(self):
        Calculations which convert apehilion to AU go here
        return result

class Ampere(SIUnit):
    def to_volts(self, wattage):
        return self.value / wattage