MNT: Use WeakKeyDictionary and WeakSet in Grouper

Rather than handling the weakrefs ourselves, just use the
builtin WeakKeyDictionary instead. This will automatically
remove dead references meaning we can remove the clean() method.

Author: greglucas

doc/api/next_api_changes/deprecations/25352-GL.rst

@@ -0,0 +1,4 @@
+``Grouper.clean()``
+~~~~~~~~~~~~~~~~~~~
+
+with no replacement. The Grouper class now cleans itself up automatically.

lib/matplotlib/axes/_base.py

@@ -1363,8 +1363,6 @@ def __clear(self):
         self.xaxis.set_clip_path(self.patch)
         self.yaxis.set_clip_path(self.patch)
 
-        self._shared_axes["x"].clean()
-        self._shared_axes["y"].clean()
         if self._sharex is not None:
             self.xaxis.set_visible(xaxis_visible)
             self.patch.set_visible(patch_visible)

lib/matplotlib/cbook.py

@@ -786,78 +786,68 @@ class Grouper:
     """
 
     def __init__(self, init=()):
-        self._mapping = {weakref.ref(x): [weakref.ref(x)] for x in init}
+        self._mapping = weakref.WeakKeyDictionary(
+            {x: weakref.WeakSet([x]) for x in init})
 
     def __getstate__(self):
         return {
             **vars(self),
             # Convert weak refs to strong ones.
-            "_mapping": {k(): [v() for v in vs] for k, vs in self._mapping.items()},
+            "_mapping": {k: set(v) for k, v in self._mapping.items()},
         }
 
     def __setstate__(self, state):
         vars(self).update(state)
         # Convert strong refs to weak ones.
-        self._mapping = {weakref.ref(k): [*map(weakref.ref, vs)]
-                         for k, vs in self._mapping.items()}
+        self._mapping = weakref.WeakKeyDictionary(
+            {k: weakref.WeakSet(v) for k, v in self._mapping.items()})
 
     def __contains__(self, item):
-        return weakref.ref(item) in self._mapping
+        return item in self._mapping
 
+    @_api.deprecated("3.8", alternative="none, you no longer need to clean a Grouper")
     def clean(self):
         """Clean dead weak references from the dictionary."""
-        mapping = self._mapping
-        to_drop = [key for key in mapping if key() is None]
-        for key in to_drop:
-            val = mapping.pop(key)
-            val.remove(key)
 
     def join(self, a, *args):
         """
         Join given arguments into the same set.  Accepts one or more arguments.
         """
         mapping = self._mapping
-        set_a = mapping.setdefault(weakref.ref(a), [weakref.ref(a)])
+        set_a = mapping.setdefault(a, weakref.WeakSet([a]))
 
         for arg in args:
-            set_b = mapping.get(weakref.ref(arg), [weakref.ref(arg)])
+            set_b = mapping.get(arg, weakref.WeakSet([arg]))
             if set_b is not set_a:
                 if len(set_b) > len(set_a):
                     set_a, set_b = set_b, set_a
-                set_a.extend(set_b)
+                set_a.update(set_b)
                 for elem in set_b:
                     mapping[elem] = set_a
 
-        self.clean()
-
     def joined(self, a, b):
         """Return whether *a* and *b* are members of the same set."""
-        self.clean()
-        return (self._mapping.get(weakref.ref(a), object())
-                is self._mapping.get(weakref.ref(b)))
+        return (self._mapping.get(a, object()) is self._mapping.get(b))
 
     def remove(self, a):
-        self.clean()
-        set_a = self._mapping.pop(weakref.ref(a), None)
+        set_a = self._mapping.pop(a, None)
         if set_a:
-            set_a.remove(weakref.ref(a))
+            set_a.remove(a)
 
     def __iter__(self):
         """
         Iterate over each of the disjoint sets as a list.
 
         The iterator is invalid if interleaved with calls to join().
         """
-        self.clean()
         unique_groups = {id(group): group for group in self._mapping.values()}
         for group in unique_groups.values():
-            yield [x() for x in group]
+            yield [x for x in group]
 
     def get_siblings(self, a):
         """Return all of the items joined with *a*, including itself."""
-        self.clean()
-        siblings = self._mapping.get(weakref.ref(a), [weakref.ref(a)])
-        return [x() for x in siblings]
+        siblings = self._mapping.get(a, [a])
+        return [x for x in siblings]
 
 
 class GrouperView:

lib/matplotlib/tests/test_cbook.py

@@ -1,7 +1,6 @@
 import itertools
 import pickle
 
-from weakref import ref
 from unittest.mock import patch, Mock
 
 from datetime import datetime, date, timedelta
@@ -590,11 +589,11 @@ class Dummy:
     mapping = g._mapping
 
     for o in objs:
-        assert ref(o) in mapping
+        assert o in mapping
 
-    base_set = mapping[ref(objs[0])]
+    base_set = mapping[objs[0]]
     for o in objs[1:]:
-        assert mapping[ref(o)] is base_set
+        assert mapping[o] is base_set
 
 
 def test_flatiter():

lib/mpl_toolkits/mplot3d/axes3d.py

@@ -640,7 +640,6 @@ def autoscale_view(self, tight=None, scalex=True, scaley=True,
             _tight = self._tight = bool(tight)
 
         if scalex and self.get_autoscalex_on():
-            self._shared_axes["x"].clean()
             x0, x1 = self.xy_dataLim.intervalx
             xlocator = self.xaxis.get_major_locator()
             x0, x1 = xlocator.nonsingular(x0, x1)
@@ -653,7 +652,6 @@ def autoscale_view(self, tight=None, scalex=True, scaley=True,
             self.set_xbound(x0, x1)
 
         if scaley and self.get_autoscaley_on():
-            self._shared_axes["y"].clean()
             y0, y1 = self.xy_dataLim.intervaly
             ylocator = self.yaxis.get_major_locator()
             y0, y1 = ylocator.nonsingular(y0, y1)
@@ -666,7 +664,6 @@ def autoscale_view(self, tight=None, scalex=True, scaley=True,
             self.set_ybound(y0, y1)
 
         if scalez and self.get_autoscalez_on():
-            self._shared_axes["z"].clean()
             z0, z1 = self.zz_dataLim.intervalx
             zlocator = self.zaxis.get_major_locator()
             z0, z1 = zlocator.nonsingular(z0, z1)