We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Stop using ABC in Serializer
AbstractSerializer is currently written as an abstract base class. I don't think it is needed to support ABC.

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `chainer/serializer.py`
Content:
```
1 import abc
2 
3 import six
4 
5 
6 @six.add_metaclass(abc.ABCMeta)
7 class AbstractSerializer(object):
8 
9     """Abstract base class of all serializers and deserializers."""
10 
11     @abc.abstractmethod
12     def __getitem__(self, key):
13         """Gets a child serializer.
14 
15         This operator creates a _child_ serializer represented by the given
16         key.
17 
18         Args:
19             key (str): Name of the child serializer.
20 
21         """
22         raise NotImplementedError
23 
24     @abc.abstractmethod
25     def __call__(self, key, value):
26         """Serializes or deserializes a value by given name.
27 
28         This operator saves or loads a value by given name.
29 
30         If this is a serializer, then the value is simply saved at the key.
31         Note that some type information might be missed depending on the
32         implementation (and the target file format).
33 
34         If this is a deserializer, then the value is loaded by the key. The
35         deserialization differently works on scalars and arrays. For scalars,
36         the ``value`` argument is used just for determining the type of
37         restored value to be converted, and the converted value is returned.
38         For arrays, the restored elements are directly copied into the
39         ``value`` argument. String values are treated like scalars. If the
40         ``value`` argument is ``None``, the type of the restored value will
41         typically be a numpy array but can depend on the particular subclass
42         implementation.
43 
44         Args:
45             key (str): Name of the serialization entry.
46             value (scalar, array, None, or str): Object to be (de)serialized.
47                 ``None`` is only supported by deserializers.
48 
49         Returns:
50             Serialized or deserialized value.
51 
52         """
53         raise NotImplementedError
54 
55 
56 class Serializer(AbstractSerializer):
57 
58     """Base class of all serializers."""
59 
60     def save(self, obj):
61         """Saves an object by this serializer.
62 
63         This is equivalent to ``obj.serialize(self)``.
64 
65         Args:
66             obj: Target object to be serialized.
67 
68         """
69         obj.serialize(self)
70 
71 
72 class Deserializer(AbstractSerializer):
73 
74     """Base class of all deserializers."""
75 
76     def load(self, obj):
77         """Loads an object from this deserializer.
78 
79         This is equivalent to ``obj.serialize(self)``.
80 
81         Args:
82             obj: Target object to be serialized.
83 
84         """
85         obj.serialize(self)
86
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/chainer/serializer.py b/chainer/serializer.py
--- a/chainer/serializer.py
+++ b/chainer/serializer.py
@@ -1,14 +1,7 @@
-import abc
-
-import six
-
-
-@six.add_metaclass(abc.ABCMeta)
 class AbstractSerializer(object):
 
     """Abstract base class of all serializers and deserializers."""
 
-    @abc.abstractmethod
     def __getitem__(self, key):
         """Gets a child serializer.
 
@@ -21,7 +14,6 @@
         """
         raise NotImplementedError
 
-    @abc.abstractmethod
     def __call__(self, key, value):
         """Serializes or deserializes a value by given name.

{"golden_diff": "diff --git a/chainer/serializer.py b/chainer/serializer.py\n--- a/chainer/serializer.py\n+++ b/chainer/serializer.py\n@@ -1,14 +1,7 @@\n-import abc\n-\n-import six\n-\n-\n-@six.add_metaclass(abc.ABCMeta)\n class AbstractSerializer(object):\n \n     \"\"\"Abstract base class of all serializers and deserializers.\"\"\"\n \n-    @abc.abstractmethod\n     def __getitem__(self, key):\n         \"\"\"Gets a child serializer.\n \n@@ -21,7 +14,6 @@\n         \"\"\"\n         raise NotImplementedError\n \n-    @abc.abstractmethod\n     def __call__(self, key, value):\n         \"\"\"Serializes or deserializes a value by given name.\n", "issue": "Stop using ABC in Serializer\nAbstractSerializer is currently written as an abstract base class. I don't think it is needed to support ABC.\n", "before_files": [{"content": "import abc\n\nimport six\n\n\n@six.add_metaclass(abc.ABCMeta)\nclass AbstractSerializer(object):\n\n    \"\"\"Abstract base class of all serializers and deserializers.\"\"\"\n\n    @abc.abstractmethod\n    def __getitem__(self, key):\n        \"\"\"Gets a child serializer.\n\n        This operator creates a _child_ serializer represented by the given\n        key.\n\n        Args:\n            key (str): Name of the child serializer.\n\n        \"\"\"\n        raise NotImplementedError\n\n    @abc.abstractmethod\n    def __call__(self, key, value):\n        \"\"\"Serializes or deserializes a value by given name.\n\n        This operator saves or loads a value by given name.\n\n        If this is a serializer, then the value is simply saved at the key.\n        Note that some type information might be missed depending on the\n        implementation (and the target file format).\n\n        If this is a deserializer, then the value is loaded by the key. The\n        deserialization differently works on scalars and arrays. For scalars,\n        the ``value`` argument is used just for determining the type of\n        restored value to be converted, and the converted value is returned.\n        For arrays, the restored elements are directly copied into the\n        ``value`` argument. String values are treated like scalars. If the\n        ``value`` argument is ``None``, the type of the restored value will\n        typically be a numpy array but can depend on the particular subclass\n        implementation.\n\n        Args:\n            key (str): Name of the serialization entry.\n            value (scalar, array, None, or str): Object to be (de)serialized.\n                ``None`` is only supported by deserializers.\n\n        Returns:\n            Serialized or deserialized value.\n\n        \"\"\"\n        raise NotImplementedError\n\n\nclass Serializer(AbstractSerializer):\n\n    \"\"\"Base class of all serializers.\"\"\"\n\n    def save(self, obj):\n        \"\"\"Saves an object by this serializer.\n\n        This is equivalent to ``obj.serialize(self)``.\n\n        Args:\n            obj: Target object to be serialized.\n\n        \"\"\"\n        obj.serialize(self)\n\n\nclass Deserializer(AbstractSerializer):\n\n    \"\"\"Base class of all deserializers.\"\"\"\n\n    def load(self, obj):\n        \"\"\"Loads an object from this deserializer.\n\n        This is equivalent to ``obj.serialize(self)``.\n\n        Args:\n            obj: Target object to be serialized.\n\n        \"\"\"\n        obj.serialize(self)\n", "path": "chainer/serializer.py"}], "after_files": [{"content": "class AbstractSerializer(object):\n\n    \"\"\"Abstract base class of all serializers and deserializers.\"\"\"\n\n    def __getitem__(self, key):\n        \"\"\"Gets a child serializer.\n\n        This operator creates a _child_ serializer represented by the given\n        key.\n\n        Args:\n            key (str): Name of the child serializer.\n\n        \"\"\"\n        raise NotImplementedError\n\n    def __call__(self, key, value):\n        \"\"\"Serializes or deserializes a value by given name.\n\n        This operator saves or loads a value by given name.\n\n        If this is a serializer, then the value is simply saved at the key.\n        Note that some type information might be missed depending on the\n        implementation (and the target file format).\n\n        If this is a deserializer, then the value is loaded by the key. The\n        deserialization differently works on scalars and arrays. For scalars,\n        the ``value`` argument is used just for determining the type of\n        restored value to be converted, and the converted value is returned.\n        For arrays, the restored elements are directly copied into the\n        ``value`` argument. String values are treated like scalars. If the\n        ``value`` argument is ``None``, the type of the restored value will\n        typically be a numpy array but can depend on the particular subclass\n        implementation.\n\n        Args:\n            key (str): Name of the serialization entry.\n            value (scalar, array, None, or str): Object to be (de)serialized.\n                ``None`` is only supported by deserializers.\n\n        Returns:\n            Serialized or deserialized value.\n\n        \"\"\"\n        raise NotImplementedError\n\n\nclass Serializer(AbstractSerializer):\n\n    \"\"\"Base class of all serializers.\"\"\"\n\n    def save(self, obj):\n        \"\"\"Saves an object by this serializer.\n\n        This is equivalent to ``obj.serialize(self)``.\n\n        Args:\n            obj: Target object to be serialized.\n\n        \"\"\"\n        obj.serialize(self)\n\n\nclass Deserializer(AbstractSerializer):\n\n    \"\"\"Base class of all deserializers.\"\"\"\n\n    def load(self, obj):\n        \"\"\"Loads an object from this deserializer.\n\n        This is equivalent to ``obj.serialize(self)``.\n\n        Args:\n            obj: Target object to be serialized.\n\n        \"\"\"\n        obj.serialize(self)\n", "path": "chainer/serializer.py"}]}