code: def get_point_from_bins_and_idx(self, chi1_bin, chi2_bin, idx):
          
          mass1 = self.massbank[chi1_bin][chi2_bin]['mass1s'][idx]
          mass2 = self.massbank[chi1_bin][chi2_bin]['mass2s'][idx]
          spin1z = self.massbank[chi1_bin][chi2_bin]['spin1s'][idx]
          spin2z = self.massbank[chi1_bin][chi2_bin]['spin2s'][idx]
          return mass1, mass2, spin1z, spin2z
docs: Find masses and spins given bin numbers and index.
  
          Given the chi1 bin, chi2 bin and an index, return the masses and spins
          of the point at that index. Will fail if no point exists there.
  
          Parameters
          -----------
          chi1_bin : int
              The bin number for chi1.
          chi2_bin : int
              The bin number for chi2.
          idx : int
              The index within the chi1, chi2 bin.
  
          Returns
          --------
          mass1 : float
              Mass of heavier body.
          mass2 : float
              Mass of lighter body.
          spin1z : float
              Spin of heavier body.
          spin2z : float
              Spin of lighter body.