MNT: use weakkeydict to manage "next number"

Author: tacaswell

mpl_gui/__init__.py

@@ -13,10 +13,10 @@
 
 """
 from collections import Counter
-from itertools import count
 import functools
 import logging
 import warnings
+from weakref import WeakKeyDictionary
 
 from matplotlib.backend_bases import FigureCanvasBase as _FigureCanvasBase
 
@@ -118,7 +118,7 @@ def __init__(self, *, block=None, timeout=0, prefix="Figure "):
         self._timeout = timeout
         self._block = block
         # Settings / state to control the default figure label
-        self._count = count()
+        self._fig_to_number = WeakKeyDictionary()
         self._prefix = prefix
         # the canonical location for storing the Figures this registry owns.
         # any additional views must never include a figure not in the list but
@@ -140,11 +140,10 @@ def _register_fig(self, fig):
         # empty string) on a Figure so if they provide duplicate labels, change
         # the labels under us, or provide a label that will be shadowed in the
         # future it will be what it is.
-        fignum = next(self._count)
+        fignum = max(self._fig_to_number.values(), default=0) + 1
         if fig.get_label() == "":
             fig.set_label(f"{self._prefix}{fignum:d}")
-        # TODO: is there a better way to track this than monkey patching?
-        fig._mpl_gui_fignum = fignum
+        self._fig_to_number[fig] = fignum
         return fig
 
     @property
@@ -194,7 +193,7 @@ def subplot_mosaic(self, *args, **kwargs):
     def _ensure_all_figures_promoted(self):
         for f in self.figures:
             if f.canvas.manager is None:
-                promote_figure(f, num=f._mpl_gui_fignum)
+                promote_figure(f, num=self._fig_to_number[f])
 
     def show_all(self, *, block=None, timeout=None):
         """