Implement Path.__deepcopy__ avoiding infinite recursion

jkseppan · jkseppan · commit 6689cc7132d3 · 2025-06-23T10:22:25.000+03:00
To deep copy an object without calling deepcopy on the object itself, create a new object of the correct class and iterate calling deepcopy on its __dict__. Closes #29157 without relying on private CPython methods. Does not fix the other issue with TransformNode.__copy__.
diff --git a/lib/matplotlib/path.py b/lib/matplotlib/path.py
@@ -16,6 +16,7 @@
 import numpy as np
 
 import matplotlib as mpl
+
 from . import _api, _path
 from .cbook import _to_unmasked_float_array, simple_linear_interpolation
 from .bezier import BezierSegment
@@ -280,8 +281,17 @@ def __deepcopy__(self, memo=None):
         Return a deepcopy of the `Path`.  The `Path` will not be
         readonly, even if the source `Path` is.
         """
-        # Deepcopying arrays (vertices, codes) strips the writeable=False flag.
-        p = copy.deepcopy(super(), memo)
+        memo = memo or {}
+        if id(self) in memo:
+            return memo[id(self)]
+
+        cls = type(self)
+        p = cls.__new__(cls)
+        memo[id(self)] = p
+
+        for k, v in self.__dict__.items():
+            setattr(p, k, copy.deepcopy(v, memo))
+
         p._readonly = False
         return p
 
diff --git a/lib/matplotlib/tests/test_path.py b/lib/matplotlib/tests/test_path.py
@@ -355,15 +355,22 @@ def test_path_deepcopy():
     # Should not raise any error
     verts = [[0, 0], [1, 1]]
     codes = [Path.MOVETO, Path.LINETO]
-    path1 = Path(verts)
-    path2 = Path(verts, codes)
+    path1 = Path(verts, readonly=True)
+    path2 = Path(verts, codes, readonly=True)
     path1_copy = path1.deepcopy()
     path2_copy = path2.deepcopy()
     assert path1 is not path1_copy
     assert path1.vertices is not path1_copy.vertices
+    assert np.all(path1.vertices == path1_copy.vertices)
+    assert path1.readonly
+    assert not path1_copy.readonly
     assert path2 is not path2_copy
     assert path2.vertices is not path2_copy.vertices
+    assert np.all(path2.vertices == path2_copy.vertices)
     assert path2.codes is not path2_copy.codes
+    assert all(path2.codes == path2_copy.codes)
+    assert path2.readonly
+    assert not path2_copy.readonly
 
 
 def test_path_shallowcopy():
