code: def _plot_filter(filters, n, eigenvalues, sum, title, ax, **kwargs):
      r
  
      if eigenvalues is None:
          eigenvalues = (filters.G._e is not None)
  
      if sum is None:
          sum = filters.n_filters > 1
  
      if title is None:
          title = repr(filters)
  
      return _plt_plot_filter(filters, n=n, eigenvalues=eigenvalues, sum=sum,
                              title=title, ax=ax, **kwargs)
docs: r"""Plot the spectral response of a filter bank.
  
      Parameters
      ----------
      n : int
          Number of points where the filters are evaluated.
      eigenvalues : boolean
          Whether to show the eigenvalues of the graph Laplacian.
          The eigenvalues should have been computed with
          :meth:`~pygsp.graphs.Graph.compute_fourier_basis`.
          By default, the eigenvalues are shown if they are available.
      sum : boolean
          Whether to plot the sum of the squared magnitudes of the filters.
          Default True if there is multiple filters.
      title : str
          Title of the figure.
      ax : :class:`matplotlib.axes.Axes`
          Axes where to draw the graph. Optional, created if not passed.
          Only available with the matplotlib backend.
      kwargs : dict
          Additional parameters passed to the matplotlib plot function.
          Useful for example to change the linewidth, linestyle, or set a label.
          Only available with the matplotlib backend.
  
      Returns
      -------
      fig : :class:`matplotlib.figure.Figure`
          The figure the plot belongs to. Only with the matplotlib backend.
      ax : :class:`matplotlib.axes.Axes`
          The axes the plot belongs to. Only with the matplotlib backend.
  
      Notes
      -----
      This function is only implemented for the matplotlib backend at the moment.
  
      Examples
      --------
      >>> import matplotlib
      >>> G = graphs.Logo()
      >>> mh = filters.MexicanHat(G)
      >>> fig, ax = mh.plot()