Backport PR #25097 on branch v3.7.x (fix FigureCanvasTkAgg memory leak via weakrefs)

lib/matplotlib/backends/_backend_tk.py

@@ -1,4 +1,5 @@
 import uuid
+import weakref
 from contextlib import contextmanager
 import logging
 import math
@@ -198,14 +199,33 @@ def __init__(self, figure=None, master=None):
         # event to the window containing the canvas instead.
         # See https://wiki.tcl-lang.org/3893 (mousewheel) for details
         root = self._tkcanvas.winfo_toplevel()
-        root.bind("<MouseWheel>", self.scroll_event_windows, "+")
+
+        # Prevent long-lived references via tkinter callback structure GH-24820
+        weakself = weakref.ref(self)
+        weakroot = weakref.ref(root)
+
+        def scroll_event_windows(event):
+            self = weakself()
+            if self is None:
+                root = weakroot()
+                if root is not None:
+                    root.unbind("<MouseWheel>", scroll_event_windows_id)
+                return
+            return self.scroll_event_windows(event)
+        scroll_event_windows_id = root.bind("<MouseWheel>", scroll_event_windows, "+")
 
         # Can't get destroy events by binding to _tkcanvas. Therefore, bind
         # to the window and filter.
         def filter_destroy(event):
+            self = weakself()
+            if self is None:
+                root = weakroot()
+                if root is not None:
+                    root.unbind("<Destroy>", filter_destroy_id)
+                return
             if event.widget is self._tkcanvas:
                 CloseEvent("close_event", self)._process()
-        root.bind("<Destroy>", filter_destroy, "+")
+        filter_destroy_id = root.bind("<Destroy>", filter_destroy, "+")
 
         self._tkcanvas.focus_set()