docs: def plot(self, key, part='re', scale='log', steps=50, legend=True, plotargs={}):
          """Plot the RG evolution of parameter `key`.
  
          Parameters:
  
          - part, scale, steps: see `plotdata`
          - legend: boolean, show the legend (default: True)
          - plotargs: dictionary of arguments to be passed to plt.plot
          """
          try:
              import matplotlib.pyplot as plt
          except ImportError:
              raise ImportError("Please install matplotlib if you want to use the plot method")
          pdat = self.plotdata(key, part=part, scale=scale, steps=steps)
          plt.plot(*pdat, label=key, **plotargs)
          if scale == 'log':
              plt.xscale('log')
          if legend:
              plt.legend()