[Solved] Converting Python Script to C++ [closed]

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When the class calls itself like that it’s the __call__ method in the class that it is calling, like operator(). __init__ is like a constructor and is called when the class is instantiated, so everything in init is available by the time the class gets to __call__.

class ReducedMomentum:
    # here is where an instance of the object calls itself
    def __call__(self, kinetic_energy):
        """Example
           reduced_momentum = ReducedMomentum(5)
           reduction = reduced_momentum(5)
        """
        return math.sqrt(kinetic_energy * (kinetic_energy + 2 * self.mass)) / self.mass

So for your Ktilde class, for example

class Ktilde:
    def __init__(self, alpha_1, tritium_mass, electron_mass_eV):
        """Constructor needing above arguments
           alpha_1: float?
           tritium_mass: float?
           electron_mass_eV: float?

           Example:
           k_tilde = Ktilde(1., 1., 1.)  # initialize with params
           some_spectator_mass = 2.  # some other relevant numbers
           some_electron_KE = 302.1
           calculation = k_tilde(some_spectator_mass, some_electron_KE)  # uses the __call__ method in this class
        """
        self.alpha_1 = alpha_1
        self.mass_fraction = MassFraction(tritium_mass, electron_mass_eV / ATOMIC_MASS)
        self.reduced_momentum = ReducedMomentum(electron_mass_eV)

    def __call__(self, spectator_mass, electron_kinetic_energy):
        return self.alpha_1 * self.mass_fraction(spectator_mass) * self.reduced_momentum(electron_kinetic_energy)

So this does

    ktilde = Ktilde(alpha_1, spectator_masses, electron_mass)  # ktilde instance
    mass_spectator = parse_spectator_mass(args, parser)  # some function to get mass of spectator
    ktilde_value = ktilde(mass_spectator, args.energy)  # uses __call__ method of KTilde, args is some object (maybe from argparser) that has an energy attribute
    print('{:.4f}'.format(ktilde_value))

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solved Converting Python Script to C++ [closed]