We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Forbid setting user and chat data attributes
Inevitably users will attempt to do `context.user_data = {'my': 'dict'}` or `context.chat_data = whatever`. This will lead to confusing behaviour.

I propose making those fields properties without a setter, which will more helpfully error. Depending on how far we want to go, we can also suggest the user to use `update(other_dict)` if they attempt to set the field.

See https://t.me/pythontelegrambotgroup/222138 onwards.

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `telegram/ext/callbackcontext.py`
Content:
```
1 #!/usr/bin/env python
2 #
3 # A library that provides a Python interface to the Telegram Bot API
4 # Copyright (C) 2015-2018
5 # Leandro Toledo de Souza <devs@python-telegram-bot.org>
6 #
7 # This program is free software: you can redistribute it and/or modify
8 # it under the terms of the GNU Lesser Public License as published by
9 # the Free Software Foundation, either version 3 of the License, or
10 # (at your option) any later version.
11 #
12 # This program is distributed in the hope that it will be useful,
13 # but WITHOUT ANY WARRANTY; without even the implied warranty of
14 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 # GNU Lesser Public License for more details.
16 #
17 # You should have received a copy of the GNU Lesser Public License
18 # along with this program.  If not, see [http://www.gnu.org/licenses/].
19 """This module contains the CallbackContext class."""
20 
21 from telegram import Update
22 
23 
24 class CallbackContext(object):
25     """
26     This is a context object passed to the callback called by :class:`telegram.ext.Handler`
27     or by the :class:`telegram.ext.Dispatcher` in an error handler added by
28     :attr:`telegram.ext.Dispatcher.add_error_handler` or to the callback of a
29     :class:`telegram.ext.Job`.
30 
31     Note:
32         :class:`telegram.ext.Dispatcher` will create a single context for an entire update. This
33         means that if you got 2 handlers in different groups and they both get called, they will
34         get passed the same `CallbackContext` object (of course with proper attributes like
35         `.matches` differing). This allows you to add custom attributes in a lower handler group
36         callback, and then subsequently access those attributes in a higher handler group callback.
37         Note that the attributes on `CallbackContext` might change in the future, so make sure to
38         use a fairly unique name for the attributes.
39 
40     Warning:
41          Do not combine custom attributes and @run_async. Due to how @run_async works, it will
42          almost certainly execute the callbacks for an update out of order, and the attributes
43          that you think you added will not be present.
44 
45     Attributes:
46         chat_data (:obj:`dict`, optional): A dict that can be used to keep any data in. For each
47             update from the same chat it will be the same ``dict``.
48         user_data (:obj:`dict`, optional): A dict that can be used to keep any data in. For each
49             update from the same user it will be the same ``dict``.
50         matches (List[:obj:`re match object`], optional): If the associated update originated from
51             a regex-supported handler or had a :class:`Filters.regex`, this will contain a list of
52             match objects for every pattern where ``re.search(pattern, string)`` returned a match.
53             Note that filters short circuit, so combined regex filters will not always
54             be evaluated.
55         args (List[:obj:`str`], optional): Arguments passed to a command if the associated update
56             is handled by :class:`telegram.ext.CommandHandler`, :class:`telegram.ext.PrefixHandler`
57             or :class:`telegram.ext.StringCommandHandler`. It contains a list of the words in the
58             text after the command, using any whitespace string as a delimiter.
59         error (:class:`telegram.TelegramError`, optional): The Telegram error that was raised.
60             Only present when passed to a error handler registered with
61             :attr:`telegram.ext.Dispatcher.add_error_handler`.
62         job (:class:`telegram.ext.Job`): The job that that originated this callback.
63             Only present when passed to the callback of :class:`telegram.ext.Job`.
64 
65     """
66 
67     def __init__(self, dispatcher):
68         """
69         Args:
70             dispatcher (:class:`telegram.ext.Dispatcher`):
71         """
72         if not dispatcher.use_context:
73             raise ValueError('CallbackContext should not be used with a non context aware '
74                              'dispatcher!')
75         self._dispatcher = dispatcher
76         self.chat_data = None
77         self.user_data = None
78         self.args = None
79         self.matches = None
80         self.error = None
81         self.job = None
82 
83     @classmethod
84     def from_error(cls, update, error, dispatcher):
85         self = cls.from_update(update, dispatcher)
86         self.error = error
87         return self
88 
89     @classmethod
90     def from_update(cls, update, dispatcher):
91         self = cls(dispatcher)
92         if update is not None and isinstance(update, Update):
93             chat = update.effective_chat
94             user = update.effective_user
95 
96             if chat:
97                 self.chat_data = dispatcher.chat_data[chat.id]
98             if user:
99                 self.user_data = dispatcher.user_data[user.id]
100         return self
101 
102     @classmethod
103     def from_job(cls, job, dispatcher):
104         self = cls(dispatcher)
105         self.job = job
106         return self
107 
108     def update(self, data):
109         self.__dict__.update(data)
110 
111     @property
112     def bot(self):
113         """:class:`telegram.Bot`: The bot associated with this context."""
114         return self._dispatcher.bot
115 
116     @property
117     def job_queue(self):
118         """
119         :class:`telegram.ext.JobQueue`: The ``JobQueue`` used by the
120             :class:`telegram.ext.Dispatcher` and (usually) the :class:`telegram.ext.Updater`
121             associated with this context.
122 
123         """
124         return self._dispatcher.job_queue
125 
126     @property
127     def update_queue(self):
128         """
129         :class:`queue.Queue`: The ``Queue`` instance used by the
130             :class:`telegram.ext.Dispatcher` and (usually) the :class:`telegram.ext.Updater`
131             associated with this context.
132 
133         """
134         return self._dispatcher.update_queue
135 
136     @property
137     def match(self):
138         """
139         `Regex match type`: The first match from :attr:`matches`.
140             Useful if you are only filtering using a single regex filter.
141             Returns `None` if :attr:`matches` is empty.
142         """
143         try:
144             return self.matches[0]  # pylint: disable=unsubscriptable-object
145         except (IndexError, TypeError):
146             return None
147
```
--- 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/telegram/ext/callbackcontext.py b/telegram/ext/callbackcontext.py
--- a/telegram/ext/callbackcontext.py
+++ b/telegram/ext/callbackcontext.py
@@ -73,13 +73,31 @@
             raise ValueError('CallbackContext should not be used with a non context aware '
                              'dispatcher!')
         self._dispatcher = dispatcher
-        self.chat_data = None
-        self.user_data = None
+        self._chat_data = None
+        self._user_data = None
         self.args = None
         self.matches = None
         self.error = None
         self.job = None
 
+    @property
+    def chat_data(self):
+        return self._chat_data
+
+    @chat_data.setter
+    def chat_data(self, value):
+        raise AttributeError("You can not assign a new value to chat_data, see "
+                             "https://git.io/fjxKe")
+
+    @property
+    def user_data(self):
+        return self._user_data
+
+    @user_data.setter
+    def user_data(self, value):
+        raise AttributeError("You can not assign a new value to user_data, see "
+                             "https://git.io/fjxKe")
+
     @classmethod
     def from_error(cls, update, error, dispatcher):
         self = cls.from_update(update, dispatcher)
@@ -94,9 +112,9 @@
             user = update.effective_user
 
             if chat:
-                self.chat_data = dispatcher.chat_data[chat.id]
+                self._chat_data = dispatcher.chat_data[chat.id]
             if user:
-                self.user_data = dispatcher.user_data[user.id]
+                self._user_data = dispatcher.user_data[user.id]
         return self
 
     @classmethod

{"golden_diff": "diff --git a/telegram/ext/callbackcontext.py b/telegram/ext/callbackcontext.py\n--- a/telegram/ext/callbackcontext.py\n+++ b/telegram/ext/callbackcontext.py\n@@ -73,13 +73,31 @@\n             raise ValueError('CallbackContext should not be used with a non context aware '\n                              'dispatcher!')\n         self._dispatcher = dispatcher\n-        self.chat_data = None\n-        self.user_data = None\n+        self._chat_data = None\n+        self._user_data = None\n         self.args = None\n         self.matches = None\n         self.error = None\n         self.job = None\n \n+    @property\n+    def chat_data(self):\n+        return self._chat_data\n+\n+    @chat_data.setter\n+    def chat_data(self, value):\n+        raise AttributeError(\"You can not assign a new value to chat_data, see \"\n+                             \"https://git.io/fjxKe\")\n+\n+    @property\n+    def user_data(self):\n+        return self._user_data\n+\n+    @user_data.setter\n+    def user_data(self, value):\n+        raise AttributeError(\"You can not assign a new value to user_data, see \"\n+                             \"https://git.io/fjxKe\")\n+\n     @classmethod\n     def from_error(cls, update, error, dispatcher):\n         self = cls.from_update(update, dispatcher)\n@@ -94,9 +112,9 @@\n             user = update.effective_user\n \n             if chat:\n-                self.chat_data = dispatcher.chat_data[chat.id]\n+                self._chat_data = dispatcher.chat_data[chat.id]\n             if user:\n-                self.user_data = dispatcher.user_data[user.id]\n+                self._user_data = dispatcher.user_data[user.id]\n         return self\n \n     @classmethod\n", "issue": "Forbid setting user and chat data attributes\nInevitably users will attempt to do `context.user_data = {'my': 'dict'}` or `context.chat_data = whatever`. This will lead to confusing behaviour.\r\n\r\nI propose making those fields properties without a setter, which will more helpfully error. Depending on how far we want to go, we can also suggest the user to use `update(other_dict)` if they attempt to set the field.\r\n\r\nSee https://t.me/pythontelegrambotgroup/222138 onwards.\n", "before_files": [{"content": "#!/usr/bin/env python\n#\n# A library that provides a Python interface to the Telegram Bot API\n# Copyright (C) 2015-2018\n# Leandro Toledo de Souza <devs@python-telegram-bot.org>\n#\n# This program is free software: you can redistribute it and/or modify\n# it under the terms of the GNU Lesser Public License as published by\n# the Free Software Foundation, either version 3 of the License, or\n# (at your option) any later version.\n#\n# This program is distributed in the hope that it will be useful,\n# but WITHOUT ANY WARRANTY; without even the implied warranty of\n# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the\n# GNU Lesser Public License for more details.\n#\n# You should have received a copy of the GNU Lesser Public License\n# along with this program.  If not, see [http://www.gnu.org/licenses/].\n\"\"\"This module contains the CallbackContext class.\"\"\"\n\nfrom telegram import Update\n\n\nclass CallbackContext(object):\n    \"\"\"\n    This is a context object passed to the callback called by :class:`telegram.ext.Handler`\n    or by the :class:`telegram.ext.Dispatcher` in an error handler added by\n    :attr:`telegram.ext.Dispatcher.add_error_handler` or to the callback of a\n    :class:`telegram.ext.Job`.\n\n    Note:\n        :class:`telegram.ext.Dispatcher` will create a single context for an entire update. This\n        means that if you got 2 handlers in different groups and they both get called, they will\n        get passed the same `CallbackContext` object (of course with proper attributes like\n        `.matches` differing). This allows you to add custom attributes in a lower handler group\n        callback, and then subsequently access those attributes in a higher handler group callback.\n        Note that the attributes on `CallbackContext` might change in the future, so make sure to\n        use a fairly unique name for the attributes.\n\n    Warning:\n         Do not combine custom attributes and @run_async. Due to how @run_async works, it will\n         almost certainly execute the callbacks for an update out of order, and the attributes\n         that you think you added will not be present.\n\n    Attributes:\n        chat_data (:obj:`dict`, optional): A dict that can be used to keep any data in. For each\n            update from the same chat it will be the same ``dict``.\n        user_data (:obj:`dict`, optional): A dict that can be used to keep any data in. For each\n            update from the same user it will be the same ``dict``.\n        matches (List[:obj:`re match object`], optional): If the associated update originated from\n            a regex-supported handler or had a :class:`Filters.regex`, this will contain a list of\n            match objects for every pattern where ``re.search(pattern, string)`` returned a match.\n            Note that filters short circuit, so combined regex filters will not always\n            be evaluated.\n        args (List[:obj:`str`], optional): Arguments passed to a command if the associated update\n            is handled by :class:`telegram.ext.CommandHandler`, :class:`telegram.ext.PrefixHandler`\n            or :class:`telegram.ext.StringCommandHandler`. It contains a list of the words in the\n            text after the command, using any whitespace string as a delimiter.\n        error (:class:`telegram.TelegramError`, optional): The Telegram error that was raised.\n            Only present when passed to a error handler registered with\n            :attr:`telegram.ext.Dispatcher.add_error_handler`.\n        job (:class:`telegram.ext.Job`): The job that that originated this callback.\n            Only present when passed to the callback of :class:`telegram.ext.Job`.\n\n    \"\"\"\n\n    def __init__(self, dispatcher):\n        \"\"\"\n        Args:\n            dispatcher (:class:`telegram.ext.Dispatcher`):\n        \"\"\"\n        if not dispatcher.use_context:\n            raise ValueError('CallbackContext should not be used with a non context aware '\n                             'dispatcher!')\n        self._dispatcher = dispatcher\n        self.chat_data = None\n        self.user_data = None\n        self.args = None\n        self.matches = None\n        self.error = None\n        self.job = None\n\n    @classmethod\n    def from_error(cls, update, error, dispatcher):\n        self = cls.from_update(update, dispatcher)\n        self.error = error\n        return self\n\n    @classmethod\n    def from_update(cls, update, dispatcher):\n        self = cls(dispatcher)\n        if update is not None and isinstance(update, Update):\n            chat = update.effective_chat\n            user = update.effective_user\n\n            if chat:\n                self.chat_data = dispatcher.chat_data[chat.id]\n            if user:\n                self.user_data = dispatcher.user_data[user.id]\n        return self\n\n    @classmethod\n    def from_job(cls, job, dispatcher):\n        self = cls(dispatcher)\n        self.job = job\n        return self\n\n    def update(self, data):\n        self.__dict__.update(data)\n\n    @property\n    def bot(self):\n        \"\"\":class:`telegram.Bot`: The bot associated with this context.\"\"\"\n        return self._dispatcher.bot\n\n    @property\n    def job_queue(self):\n        \"\"\"\n        :class:`telegram.ext.JobQueue`: The ``JobQueue`` used by the\n            :class:`telegram.ext.Dispatcher` and (usually) the :class:`telegram.ext.Updater`\n            associated with this context.\n\n        \"\"\"\n        return self._dispatcher.job_queue\n\n    @property\n    def update_queue(self):\n        \"\"\"\n        :class:`queue.Queue`: The ``Queue`` instance used by the\n            :class:`telegram.ext.Dispatcher` and (usually) the :class:`telegram.ext.Updater`\n            associated with this context.\n\n        \"\"\"\n        return self._dispatcher.update_queue\n\n    @property\n    def match(self):\n        \"\"\"\n        `Regex match type`: The first match from :attr:`matches`.\n            Useful if you are only filtering using a single regex filter.\n            Returns `None` if :attr:`matches` is empty.\n        \"\"\"\n        try:\n            return self.matches[0]  # pylint: disable=unsubscriptable-object\n        except (IndexError, TypeError):\n            return None\n", "path": "telegram/ext/callbackcontext.py"}], "after_files": [{"content": "#!/usr/bin/env python\n#\n# A library that provides a Python interface to the Telegram Bot API\n# Copyright (C) 2015-2018\n# Leandro Toledo de Souza <devs@python-telegram-bot.org>\n#\n# This program is free software: you can redistribute it and/or modify\n# it under the terms of the GNU Lesser Public License as published by\n# the Free Software Foundation, either version 3 of the License, or\n# (at your option) any later version.\n#\n# This program is distributed in the hope that it will be useful,\n# but WITHOUT ANY WARRANTY; without even the implied warranty of\n# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the\n# GNU Lesser Public License for more details.\n#\n# You should have received a copy of the GNU Lesser Public License\n# along with this program.  If not, see [http://www.gnu.org/licenses/].\n\"\"\"This module contains the CallbackContext class.\"\"\"\n\nfrom telegram import Update\n\n\nclass CallbackContext(object):\n    \"\"\"\n    This is a context object passed to the callback called by :class:`telegram.ext.Handler`\n    or by the :class:`telegram.ext.Dispatcher` in an error handler added by\n    :attr:`telegram.ext.Dispatcher.add_error_handler` or to the callback of a\n    :class:`telegram.ext.Job`.\n\n    Note:\n        :class:`telegram.ext.Dispatcher` will create a single context for an entire update. This\n        means that if you got 2 handlers in different groups and they both get called, they will\n        get passed the same `CallbackContext` object (of course with proper attributes like\n        `.matches` differing). This allows you to add custom attributes in a lower handler group\n        callback, and then subsequently access those attributes in a higher handler group callback.\n        Note that the attributes on `CallbackContext` might change in the future, so make sure to\n        use a fairly unique name for the attributes.\n\n    Warning:\n         Do not combine custom attributes and @run_async. Due to how @run_async works, it will\n         almost certainly execute the callbacks for an update out of order, and the attributes\n         that you think you added will not be present.\n\n    Attributes:\n        chat_data (:obj:`dict`, optional): A dict that can be used to keep any data in. For each\n            update from the same chat it will be the same ``dict``.\n        user_data (:obj:`dict`, optional): A dict that can be used to keep any data in. For each\n            update from the same user it will be the same ``dict``.\n        matches (List[:obj:`re match object`], optional): If the associated update originated from\n            a regex-supported handler or had a :class:`Filters.regex`, this will contain a list of\n            match objects for every pattern where ``re.search(pattern, string)`` returned a match.\n            Note that filters short circuit, so combined regex filters will not always\n            be evaluated.\n        args (List[:obj:`str`], optional): Arguments passed to a command if the associated update\n            is handled by :class:`telegram.ext.CommandHandler`, :class:`telegram.ext.PrefixHandler`\n            or :class:`telegram.ext.StringCommandHandler`. It contains a list of the words in the\n            text after the command, using any whitespace string as a delimiter.\n        error (:class:`telegram.TelegramError`, optional): The Telegram error that was raised.\n            Only present when passed to a error handler registered with\n            :attr:`telegram.ext.Dispatcher.add_error_handler`.\n        job (:class:`telegram.ext.Job`): The job that that originated this callback.\n            Only present when passed to the callback of :class:`telegram.ext.Job`.\n\n    \"\"\"\n\n    def __init__(self, dispatcher):\n        \"\"\"\n        Args:\n            dispatcher (:class:`telegram.ext.Dispatcher`):\n        \"\"\"\n        if not dispatcher.use_context:\n            raise ValueError('CallbackContext should not be used with a non context aware '\n                             'dispatcher!')\n        self._dispatcher = dispatcher\n        self._chat_data = None\n        self._user_data = None\n        self.args = None\n        self.matches = None\n        self.error = None\n        self.job = None\n\n    @property\n    def chat_data(self):\n        return self._chat_data\n\n    @chat_data.setter\n    def chat_data(self, value):\n        raise AttributeError(\"You can not assign a new value to chat_data, see \"\n                             \"https://git.io/fjxKe\")\n\n    @property\n    def user_data(self):\n        return self._user_data\n\n    @user_data.setter\n    def user_data(self, value):\n        raise AttributeError(\"You can not assign a new value to user_data, see \"\n                             \"https://git.io/fjxKe\")\n\n    @classmethod\n    def from_error(cls, update, error, dispatcher):\n        self = cls.from_update(update, dispatcher)\n        self.error = error\n        return self\n\n    @classmethod\n    def from_update(cls, update, dispatcher):\n        self = cls(dispatcher)\n        if update is not None and isinstance(update, Update):\n            chat = update.effective_chat\n            user = update.effective_user\n\n            if chat:\n                self._chat_data = dispatcher.chat_data[chat.id]\n            if user:\n                self._user_data = dispatcher.user_data[user.id]\n        return self\n\n    @classmethod\n    def from_job(cls, job, dispatcher):\n        self = cls(dispatcher)\n        self.job = job\n        return self\n\n    def update(self, data):\n        self.__dict__.update(data)\n\n    @property\n    def bot(self):\n        \"\"\":class:`telegram.Bot`: The bot associated with this context.\"\"\"\n        return self._dispatcher.bot\n\n    @property\n    def job_queue(self):\n        \"\"\"\n        :class:`telegram.ext.JobQueue`: The ``JobQueue`` used by the\n            :class:`telegram.ext.Dispatcher` and (usually) the :class:`telegram.ext.Updater`\n            associated with this context.\n\n        \"\"\"\n        return self._dispatcher.job_queue\n\n    @property\n    def update_queue(self):\n        \"\"\"\n        :class:`queue.Queue`: The ``Queue`` instance used by the\n            :class:`telegram.ext.Dispatcher` and (usually) the :class:`telegram.ext.Updater`\n            associated with this context.\n\n        \"\"\"\n        return self._dispatcher.update_queue\n\n    @property\n    def match(self):\n        \"\"\"\n        `Regex match type`: The first match from :attr:`matches`.\n            Useful if you are only filtering using a single regex filter.\n            Returns `None` if :attr:`matches` is empty.\n        \"\"\"\n        try:\n            return self.matches[0]  # pylint: disable=unsubscriptable-object\n        except (IndexError, TypeError):\n            return None\n", "path": "telegram/ext/callbackcontext.py"}]}