text: 
  proton = 1.00727647
  neutron = 1.008664
  
  class Atom:
  
  
      @property
      def atomic_mass(self):
          mass = 0
          for m, a in self.isotopes:
              p = self.num
              n = m-p
              print(p, n)
              mass += ((p*proton) + n*neutron) *a
          return mass
  
  
  class Hydrogen(Atom):
      valene = 1
      radius = 0.25
      num = 1
      mass = 1
      isotopes = [(1, .999885), (2, 0.000115)]
  
  class Helium(Atom):
      valence = 0
      radius = 31
      num = 2
      mass = 4
      isotopes = [(3, 0.00000134), (4, 0.99999866)]
  
  
  class Carbon(Atom):
      valence = 4
      radius = 0.7
      num = 6
      mass = 12
      isotopes = [(12, 0.9893), (13, 0.0107)]
  
  
  
  if __name__ == '__main__':
      c = Carbon()
  
      h = Hydrogen()
      print(h.isotopes)
      print( h.atomic_mass)
      print(c.atomic_mass)