Simplify maxdict implementation.

anntzer · anntzer · commit b8be3853b74b · 2021-03-20T14:57:56.000+01:00
... by relying on dicts maintaining insertion order (which is what was
previously tracked separately in `_killkeys`).

Note that both the original and new implementations actually evict keys
by *insertion* order, not as LRU.
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -584,18 +584,15 @@ class maxdict(dict):
     This doesn't override all the relevant methods to constrain the size,
     just ``__setitem__``, so use with caution.
     """
+
     def __init__(self, maxsize):
-        dict.__init__(self)
+        super().__init__()
         self.maxsize = maxsize
-        self._killkeys = []
 
     def __setitem__(self, k, v):
-        if k not in self:
-            if len(self) >= self.maxsize:
-                del self[self._killkeys[0]]
-                del self._killkeys[0]
-            self._killkeys.append(k)
-        dict.__setitem__(self, k, v)
+        super().__setitem__(k, v)
+        while len(self) >= self.maxsize:
+            del self[next(iter(self))]
 
 
 class Stack:
