Fix pure python multidict.extend() version

Author: asvetlov

aiohttp/multidict.py

@@ -178,14 +178,20 @@ def _extend(self, args, kwargs, name, method):
             raise TypeError("{} takes at most 1 positional argument"
                             " ({} given)".format(name, len(args)))
         if args:
+            arg = args[0]
             if isinstance(args[0], _MultiDictProxy):
-                items = args[0].items()
+                items = arg._items
             elif isinstance(args[0], _MultiDict):
-                items = args[0].items()
-            elif hasattr(args[0], 'items'):
-                items = args[0].items()
+                items = arg._items
+            elif hasattr(arg, 'items'):
+                items = arg.items()
             else:
-                items = args[0]
+                for item in arg:
+                    if not len(item) == 2:
+                        raise TypeError(
+                            "{} takes either dict or list of (key, value) "
+                            "tuples".format(name))
+                items = arg
 
             for key, value in items:
                 method(key, value)

tests/test_multidict.py

@@ -290,7 +290,7 @@ def test_extend_with_upstr(self):
         us = self.upstr_cls('a')
         d = self.make_dict()
 
-        d.extend((us, 'val'))
+        d.extend([(us, 'val')])
         self.assertEqual([('A', 'val')], list(d.items()))