code: def _add_labels(self, axes, dtype):
          
          for ax in axes[1, :].flat:
              ax.set_xlabel('frequency [Hz]')
  
          if dtype == 'rho':
              axes[0, 0].set_ylabel(r'$|\rho| [\Omega m]$')
              axes[0, 1].set_ylabel(r'$-\phi [mrad]$')
              axes[1, 0].set_ylabel(r"$\sigma' [S/m]$")
              axes[1, 1].set_ylabel(r"$\sigma'' [S/m]$")
          elif dtype == 'r':
              axes[0, 0].set_ylabel(r'$|R| [\Omega]$')
              axes[0, 1].set_ylabel(r'$-\phi [mrad]$')
              axes[1, 0].set_ylabel(r"$Y' [S]$")
              axes[1, 1].set_ylabel(r"$Y'' [S]$")
          else:
              raise Exception('dtype not known: {}'.format(dtype))
docs: Given a 2x2 array of axes, add x and y labels
  
          Parameters
          ----------
          axes: numpy.ndarray, 2x2
              A numpy array containing the four principal axes of an SIP plot
          dtype: string
              Can be either 'rho' or 'r', indicating the type of data that is
              plotted: 'rho' stands for resistivities/conductivities, 'r' stands
              for impedances/condactances
  
          Returns
          -------
          None