updated code according to fafhrd91's comments

Author: mind1m

aiohttp/multidict.py

@@ -42,19 +42,20 @@ def getall(self, key, default=_marker):
         res = tuple([v for k, v in self._items if k == key])
         if res:
             return res
-        if not res and default != _marker:
+        if not res and default is not _marker:
             return default
         raise KeyError('Key not found: %r' % key)
 
     def getone(self, key, default=_marker):
         """
-        Get one value matching the key, raising a KeyError if multiple
-        values were found.
+        Get first value matching the key
         """
-        v = self.getall(key, default=_marker)
-        if len(v) > 1 and v != default:
-            raise KeyError('Multiple values match %r: %r' % (key, v))
-        return v[0]
+        for k, v in self._items:
+            if k == key:
+                return v
+        if default is not _marker:
+            return default
+        raise KeyError('Key not found: %r' % key)
 
     # extra methods #
 
@@ -269,12 +270,14 @@ def __init__(self, items, *, getall=False):
         super().__init__(items_to_use)
 
     def __contains__(self, value):
-        values = [item[1] for item in self._mapping]
-        return value in values
+        for item in self._mapping:
+            if item[1] == value:
+                return True
+        return False
 
     def __iter__(self):
-        values = (item[1] for item in self._mapping)
-        yield from values
+        for item in self._mapping:
+            yield item[1]
 
 
 class _KeysView(abc.KeysView):

tests/test_multidict.py

@@ -58,8 +58,7 @@ def test_instantiate__with_kwargs(self):
 
     def test_getone(self):
         d = self.make_dict([('key', 'value1')], key='value2')
-        with self.assertRaises(KeyError):
-            self.assertEqual(d.getone('key'), 'value1')
+        self.assertEqual(d.getone('key'), 'value1')
         self.assertEqual(d.get('key'), 'value1')
         self.assertEqual(d['key'], 'value1')
 
@@ -143,8 +142,7 @@ def make_dict(self, *args, **kwargs):
 
     def test_basics(self):
         d = self.make_dict([('KEY', 'value1')], KEY='value2')
-        with self.assertRaises(KeyError):
-            self.assertEqual(d.getone('key'), 'value1')
+        self.assertEqual(d.getone('key'), 'value1')
         self.assertEqual(d.get('key'), 'value1')
         self.assertEqual(d.get('key2', 'val'), 'val')
         self.assertEqual(d['key'], 'value1')