MNT: don't set method objects back onto the objects

tacaswell · tacaswell · commit 73855bfa751b · 2020-06-03T16:38:30.000-04:00
If we are monkey-patching methods then we need to be sure that when
we restore the original attribute we need to make sure we don't
stick the method instance in place (which creates a circular
reference).
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -24,6 +24,7 @@
 import types
 import warnings
 import weakref
+import inspect
 
 import numpy as np
 
@@ -2039,7 +2040,7 @@ def _setattr_cm(obj, **kwargs):
         yield
     finally:
         for attr, orig in origs:
-            if orig is sentinel:
+            if orig is sentinel or inspect.ismethod(orig):
                 delattr(obj, attr)
             else:
                 setattr(obj, attr, orig)
diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
@@ -651,3 +651,26 @@ def test_check_shape(target, test_shape):
     with pytest.raises(ValueError,
                        match=error_pattern):
         cbook._check_shape(target, aardvark=data)
+
+
+def test_setattr_cm():
+    class A:
+        def __init__(self):
+            self.aardvark = 'aardvark'
+
+        def meth(self):
+            ...
+
+    a = A()
+
+    assert id(a.meth) != id(a.meth)
+    assert id(a.aardvark) == id(a.aardvark)
+
+    with cbook._setattr_cm(a, aardvark='moose', meth=lambda: None):
+        assert id(a.meth) == id(a.meth)
+        assert id(a.aardvark) == id(a.aardvark)
+        assert a.aardvark == 'moose'
+
+    assert id(a.meth) != id(a.meth)
+    assert id(a.aardvark) == id(a.aardvark)
+    assert a.aardvark == 'aardvark'
