docstr: A generator to yield as many labels as needed, re-using existing ones
  where possible.
code: def _generate_labels(self):
      """
      A generator to yield as many labels as needed, re-using existing ones
      where possible.
      """
      for label in self._all_labels:
          yield label
  
      while True:
          # Ran out of existing labels.  Create some empty ones.
          new_artist = matplotlib.text.Text()
          new_artist.set_figure(self.axes.figure)
          new_artist.axes = self.axes
  
          new_label = Label(new_artist, None, None, None)
          self._all_labels.append(new_label)
  
          yield new_label
  
imports: import itertools
  import operator
  import warnings
  import matplotlib
  import matplotlib.artist
  import matplotlib.collections
  import matplotlib.text
  import matplotlib.ticker
  import matplotlib.transforms
  import numpy
  import shapely.geometry
  import cartopy
  from cartopy.crs import PlateCarree, Projection, _RectangularProjection
  from cartopy.mpl.ticker import LatitudeFormatter, LatitudeLocator, LongitudeFormatter, LongitudeLocator
label_desc: Use image node_id 17 for calling the Gridliner obj's underlying member method code with example usage: obj._generate_labels() without return types