docs: def plotdata(self, key, part='re', scale='log', steps=50):
          """Return a tuple of arrays x, y that can be fed to plt.plot,
          where x is the scale in GeV and y is the parameter of interest.
  
          Parameters:
  
          - key: dicionary key of the parameter to be plotted (e.g. a WCxf
            coefficient name or a SM parameter like 'g')
          - part: plot the real part 're' (default) or the imaginary part 'im'
          - scale: 'log'; make the x steps logarithmically distributed; for
            'linear', linearly distributed
          - steps: steps in x to take (default: 50)
          """
          if scale == 'log':
              x = np.logspace(log(self.scale_min),
                              log(self.scale_max),
                              steps,
                              base=e)
          elif scale == 'linear':
              x = np.linspace(self.scale_min,
                              self.scale_max,
                              steps)
          y = self.fun(x)
          y = np.array([d[key] for d in y])
          if part == 're':
              return x, y.real
          elif part == 'im':
              return x, y.imag