Fake cupy.random: no wrapped dunder names

src/cunumpy/_fake_cupy_impl.py

@@ -532,11 +532,21 @@ def __getattr__(self, name):
 
 random = types.ModuleType("cupy.random")
 random.default_rng = lambda seed=None: _RNGProxy(_np.random.default_rng(_unwrap(seed)))
-random.__getattr__ = lambda attr: _wrap_callable(
-    getattr(_np.random, attr),
-    strict=False,
-    name=f"cupy.random.{attr}",
-)
+
+
+def _random_getattr(attr):
+    # dunder names (``__file__``, ``__path__``, ...) are not NumPy functions:
+    # answering them with a wrapper breaks module introspection (astropy's import)
+    if attr.startswith("__"):
+        raise AttributeError(attr)
+    return _wrap_callable(
+        getattr(_np.random, attr),
+        strict=False,
+        name=f"cupy.random.{attr}",
+    )
+
+
+random.__getattr__ = _random_getattr
 
 for _m in (cuda, cuda.device, cuda.runtime, linalg, fft, random):
     _sys.modules[_m.__name__] = _m

tests/unit/test_fake_cupy_random.py

@@ -0,0 +1,29 @@
+"""The fake cupy.random: NumPy's random functions behind the CuPy rules."""
+
+from pathlib import Path
+
+from cunumpy.kernel_testing import run_in_fake_cupy_subprocess
+
+SRC = str(Path(__file__).resolve().parents[2] / "src")
+
+
+def test_dunder_names_are_not_wrapped():
+    """A module attribute such as ``__file__`` is not a function.
+
+    Wrapping it broke module introspection: importing astropy after cunumpy
+    failed with "'function' object has no attribute 'endswith'".
+    """
+    code = """
+import inspect
+import sys
+import cunumpy as xp
+xp.set_backend("cupy")
+random = sys.modules["cupy.random"]
+assert not callable(getattr(random, "__file__", None))
+assert not hasattr(random, "__path__")
+assert inspect.getmodule(random) is random
+assert callable(random.standard_normal)
+print("ok")
+"""
+    out = run_in_fake_cupy_subprocess(code, env={"PYTHONPATH": SRC}).stdout
+    assert "ok" in out