Intern map keys (#381)

Fixes #372.

Author: methane

msgpack/fallback.py

@@ -644,6 +644,8 @@ def _unpack(self, execute=EX_CONSTRUCT):
                     key = self._unpack(EX_CONSTRUCT)
                     if self._strict_map_key and type(key) not in (unicode, bytes):
                         raise ValueError("%s is not allowed for map key" % str(type(key)))
+                    if not PY2 and type(key) is str:
+                        key = sys.intern(key)
                     ret[key] = self._unpack(EX_CONSTRUCT)
                 if self._object_hook is not None:
                     ret = self._object_hook(ret)

msgpack/unpack.h

@@ -192,6 +192,9 @@ static inline int unpack_callback_map_item(unpack_user* u, unsigned int current,
         PyErr_Format(PyExc_ValueError, "%.100s is not allowed for map key", Py_TYPE(k)->tp_name);
         return -1;
     }
+    if (PyUnicode_CheckExact(k)) {
+        PyUnicode_InternInPlace(&k);
+    }
     if (u->has_pairs_hook) {
         msgpack_unpack_object item = PyTuple_Pack(2, k, v);
         if (!item)