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BTrees/BTreeModuleTemplate.c

@@ -559,11 +559,14 @@ module_init(void)
                 "persistent.cPersistence", "CAPI");
 #endif
     if (cPersistenceCAPI == NULL) {
-       /* At least some versions of Python 3.5 raise an AttribteError
-        * an ImportError here:  re-map as an ImportError for compatibility.
+       /* The Capsule API attempts to import 'persistent' and then
+        * walk down to the specified attribute using getattr. If the C
+        * extensions aren't available, this can result in an
+        * AttributeError being raised. Let that percolate up as an
+        * ImportError so it can be caught in the expected way.
         */
        if (PyErr_Occurred() && !PyErr_ExceptionMatches(PyExc_ImportError)) {
-           PyErr_SetString(PyExc_ImportError, "<No CPersistence>");
+           PyErr_SetString(PyExc_ImportError, "persistent C extension unavailable");
        }
         return NULL;
    }

CHANGES.rst

@@ -5,6 +5,10 @@
 ------------------
 
 - Add support for Python 3.6.
+- Raise an ``ImportError`` consistently on Python 3 if the C extension for
+  BTrees is used but the ``persistent`` C extension is not available.
+  Previously this could result in an odd ``AttributeError``. See
+  https://github.com/zopefoundation/BTrees/pull/55
 
 4.4.0 (2017-01-11)
 ------------------