Fake cupyx.scipy: copy and deepcopy of proxy objects

CHANGELOG.md

@@ -45,6 +45,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   warnings as errors. Docstring style: `docs/source/contributing.md`.
 
 ### Fixed
+- Splines and other objects of the fake `cupyx.scipy` can be copied with
+  `copy.copy` and `copy.deepcopy` (also inside a copied container), as real
+  CuPy splines can.
 - `xp.algorithms.segment_sum` and `SegmentPlan.sum` work on the fake CuPy: it
   cannot compile the CUDA kernel, so the sum runs on the host buffers of the
   fake arrays and the CuPy path of a program runs without a GPU.

src/cunumpy/_fake_cupyx.py

@@ -21,6 +21,7 @@
 
 from __future__ import annotations
 
+import copy
 import importlib
 import sys
 import types
@@ -263,6 +264,14 @@ def __call__(self, *args: Any, **kwargs: Any) -> Any:
     def __repr__(self) -> str:
         return f"<fake cupyx {self._obj!r}>"
 
+    # copies wrap a copy of the SciPy object and share the fake CuPy module (a
+    # module cannot be copied), as real CuPy splines can be copied
+    def __copy__(self) -> _Proxy:
+        return _Proxy(copy.copy(self._obj), self._cupy)
+
+    def __deepcopy__(self, memo: dict) -> _Proxy:
+        return _Proxy(copy.deepcopy(self._obj, memo), self._cupy)
+
 
 class _ProxyClass:
     """A SciPy class seen as a CuPy class: instances are :class:`_Proxy`."""

tests/unit/test_fake_cupyx.py

@@ -48,6 +48,26 @@ def test_splines_fit_and_evaluate_on_the_device():
     assert "ok" in run(code)
 
 
+def test_splines_can_be_copied():
+    code = """
+import copy
+import numpy as np
+import cunumpy as xp
+xp.set_backend("cupy")
+x = xp.linspace(0.0, 1.0, 11)
+spl = xp.scipy.interpolate.UnivariateSpline(x, xp.sin(3 * x), k=3, s=0.0, ext=3)
+for c in (copy.copy(spl), copy.deepcopy(spl), copy.deepcopy({"spline": spl})["spline"]):
+    assert isinstance(c, xp.scipy.interpolate.UnivariateSpline)
+    assert xp.is_gpu(c(x))
+    assert np.array_equal(xp.to_numpy(c(x)), xp.to_numpy(spl(x)))
+# a deep copy is independent of the original
+c = copy.deepcopy(spl)
+assert c._obj is not spl._obj
+print("ok")
+"""
+    assert "ok" in run(code)
+
+
 def test_host_arrays_are_rejected_like_cupy():
     code = """
 import numpy as np