code: def draw_identity_line(ax=None, dynamic=True, **kwargs):
      
  
      # Get the current working axes
      ax = ax or plt.gca()
  
      # Define the standard line color
      if 'c' not in kwargs and 'color' not in kwargs:
          kwargs['color'] = LINE_COLOR
  
      # Define the standard opacity
      if 'alpha' not in kwargs:
          kwargs['alpha'] = 0.5
  
      # Draw the identity line
      identity, = ax.plot([],[], **kwargs)
  
      # Define the callback
      def callback(ax):
          # Get the x and y limits on the axes
          xlim = ax.get_xlim()
          ylim = ax.get_ylim()
  
          # Set the bounding range of the line
          data = (
              max(xlim[0], ylim[0]), min(xlim[1], ylim[1])
          )
          identity.set_data(data, data)
  
      # Register the callback and return
      callback(ax)
  
      if dynamic:
          ax.callbacks.connect('xlim_changed', callback)
          ax.callbacks.connect('ylim_changed', callback)
  
      return ax
docs: Draws a 45 degree identity line such that y=x for all points within the
      given axes x and y limits. This function also registeres a callback so
      that as the figure is modified, the axes are updated and the line remains
      drawn correctly.
  
      Parameters
      ----------
  
      ax : matplotlib Axes, default: None
          The axes to plot the figure on. If None is passed in the current axes
          will be used (or generated if required).
  
      dynamic : bool, default : True
          If the plot is dynamic, callbacks will be registered to update the
          identiy line as axes are changed.
  
      kwargs : dict
          Keyword arguments to pass to the matplotlib plot function to style the
          identity line.
  
  
      Returns
      -------
  
      ax : matplotlib Axes
          The axes with the line drawn on it.
  
      Notes
      -----
  
      .. seealso:: `StackOverflow discussion: Does matplotlib have a function for drawing diagonal lines in axis coordinates? <https://stackoverflow.com/questions/22104256/does-matplotlib-have-a-function-for-drawing-diagonal-lines-in-axis-coordinates>`_