Add and remove some PyPy iterator workarounds

* The definition of `PySequence_Fast` is more restrictive on PyPy, so
  use the slow path instead.
* `PyDict_Next` has been fixed in PyPy -> remove workaround.

include/pybind11/pybind11.h

@@ -1177,29 +1177,10 @@ public:
 
     /// Export enumeration entries into the parent scope
     enum_ &export_values() {
-#if !defined(PYPY_VERSION)
-        PyObject *dict = ((PyTypeObject *) this->m_ptr)->tp_dict;
-        PyObject *key, *value;
-        ssize_t pos = 0;
-
-        while (PyDict_Next(dict, &pos, &key, &value)) {
-            if (PyObject_IsInstance(value, this->m_ptr))
-                m_parent.attr(key) = value;
+        for (auto item : reinterpret_borrow<dict>(((PyTypeObject *) this->m_ptr)->tp_dict)) {
+            if (isinstance(item.second, this->m_ptr))
+                m_parent.attr(item.first) = item.second;
         }
-#else
-        /* PyPy's cpyext still has difficulties with the above
-           CPython API calls; emulate using Python code. */
-        dict d; d["t"] = *this; d["p"] = m_parent;
-        PyObject *result = PyRun_String(
-            "for k, v in t.__dict__.items():\n"
-            "    if isinstance(v, t):\n"
-            "        setattr(p, k, v)\n",
-            Py_file_input, d.ptr(), d.ptr());
-        if (result == nullptr)
-            throw error_already_set();
-        Py_DECREF(result);
-#endif
-
         return *this;
     }
 

include/pybind11/pytypes.h

@@ -613,8 +613,14 @@ private:
 };
 NAMESPACE_END(iterator_policies)
 
+#if !defined(PYPY_VERSION)
 using tuple_iterator = generic_iterator<iterator_policies::sequence_fast_readonly>;
 using list_iterator = generic_iterator<iterator_policies::sequence_fast_readonly>;
+#else
+using tuple_iterator = generic_iterator<iterator_policies::sequence_slow_readwrite>;
+using list_iterator = generic_iterator<iterator_policies::sequence_slow_readwrite>;
+#endif
+
 using sequence_iterator = generic_iterator<iterator_policies::sequence_slow_readwrite>;
 using dict_iterator = generic_iterator<iterator_policies::dict_readonly>;