Work around error that "__reduce_cython__ cannot be found" when re-importing an extension module that was already initialised before.gh3545_reduce_cython_reimport

Closes #3545.

2 files changed, 56 insertions, 6 deletions

diff --git a/Cython/Utility/ExtensionTypes.c b/Cython/Utility/ExtensionTypes.c
index efdfd35ef..a75863d02 100644
--- a/Cython/Utility/ExtensionTypes.c
+++ b/Cython/Utility/ExtensionTypes.c
@@ -235,16 +235,28 @@ static int __Pyx_setup_reduce(PyObject* type_obj) {
         reduce = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__reduce__")); if (unlikely(!reduce)) goto __PYX_BAD;
 
         if (reduce == object_reduce || __Pyx_setup_reduce_is_named(reduce, PYIDENT("__reduce_cython__"))) {
-            reduce_cython = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__reduce_cython__")); if (unlikely(!reduce_cython)) goto __PYX_BAD;
-            ret = PyDict_SetItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__reduce__"), reduce_cython); if (unlikely(ret < 0)) goto __PYX_BAD;
-            ret = PyDict_DelItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__reduce_cython__")); if (unlikely(ret < 0)) goto __PYX_BAD;
+            reduce_cython = __Pyx_PyObject_GetAttrStrNoError(type_obj, PYIDENT("__reduce_cython__"));
+            if (likely(reduce_cython)) {
+                ret = PyDict_SetItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__reduce__"), reduce_cython); if (unlikely(ret < 0)) goto __PYX_BAD;
+                ret = PyDict_DelItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__reduce_cython__")); if (unlikely(ret < 0)) goto __PYX_BAD;
+            } else if (reduce == object_reduce || PyErr_Occurred()) {
+                // Ignore if we're done, i.e. if 'reduce' already has the right name and the original is gone.
+                // Otherwise: error.
+                goto __PYX_BAD;
+            }
 
             setstate = __Pyx_PyObject_GetAttrStrNoError(type_obj, PYIDENT("__setstate__"));
             if (!setstate) PyErr_Clear();
             if (!setstate || __Pyx_setup_reduce_is_named(setstate, PYIDENT("__setstate_cython__"))) {
-                setstate_cython = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__setstate_cython__")); if (unlikely(!setstate_cython)) goto __PYX_BAD;
-                ret = PyDict_SetItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__setstate__"), setstate_cython); if (unlikely(ret < 0)) goto __PYX_BAD;
-                ret = PyDict_DelItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__setstate_cython__")); if (unlikely(ret < 0)) goto __PYX_BAD;
+                setstate_cython = __Pyx_PyObject_GetAttrStrNoError(type_obj, PYIDENT("__setstate_cython__"));
+                if (likely(setstate_cython)) {
+                    ret = PyDict_SetItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__setstate__"), setstate_cython); if (unlikely(ret < 0)) goto __PYX_BAD;
+                    ret = PyDict_DelItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__setstate_cython__")); if (unlikely(ret < 0)) goto __PYX_BAD;
+                } else if (!setstate || PyErr_Occurred()) {
+                    // Ignore if we're done, i.e. if 'setstate' already has the right name and the original is gone.
+                    // Otherwise: error.
+                    goto __PYX_BAD;
+                }
             }
             PyType_Modified((PyTypeObject*)type_obj);
         }
diff --git a/tests/run/reimport_failure.srctree b/tests/run/reimport_failure.srctree
new file mode 100644
index 000000000..498c9bd36
--- /dev/null
+++ b/tests/run/reimport_failure.srctree
@@ -0,0 +1,38 @@
+# mode: run
+# tag: pep489
+
+"""
+PYTHON setup.py build_ext -i
+PYTHON tester.py
+"""
+
+######## setup.py ########
+
+from Cython.Build.Dependencies import cythonize
+from distutils.core import setup
+
+setup(
+  ext_modules = cythonize("*.pyx"),
+)
+
+
+######## failure.pyx ########
+
+if globals():  # runtime True to confuse dead code removal
+    raise ImportError
+
+cdef class C:
+    cdef int a
+
+
+######## tester.py ########
+
+try:
+    try:
+        import failure  # 1
+    except ImportError:
+        import failure  # 2
+except ImportError:
+    pass
+else:
+    raise RuntimeError("ImportError was not raised on second import!")