Flask Server (#4433)

* Flask Demo Added

Added folder with name flask_api_dome and added code to implement parlai model with flask framework and readme file in the same folder. Also added URL to flask API folder on main README.md file.

* Update README.md

* Revert "Update README.md"

This reverts commit 1a6122d.

* Revert "Flask Demo Added"

This reverts commit 778e217.

* one the necessary changes as per suggestions

* Update requirements.txt

Added flask on  requirements.txt file

* Update index.md

* Revert "Update index.md"

This reverts commit 29eff3b.

* Revert "Update requirements.txt"

This reverts commit 4c7ac44.

* Revert "one the necessary changes as per suggestions"

This reverts commit a81ff9c.

* Deleted flask_demo.py

Code has been added to doc file, so removing it for now so solve build_website error

* Flask_demo added

* Remove Model as global model

* update tutorial_flask

* Updated tutorial_flask.md

* updated flask_demo.py

* Lint.

* Update parlai/scripts/flask_demo.py

lint again

* Update parlai/scripts/flask_demo.py

lol keep linting

* Few Changes to Improve script

* Wrap in a proper script.

* Whoops

* Lint.

Co-authored-by: Khushal Jethava <khushaljethwa14@gmail.com>
Co-authored-by: Khushal Jethava <khushaljethava14@outlook.com>

parlai/scripts/flask.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+
+# Copyright (c) Facebook, Inc. and its affiliates.
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""
+Example Flask server which hosts a model.
+
+## Examples
+**Serving the model**
+```shell
+parlai flask -m repeat_query
+parlai flask -mf zoo:blender/blender_90M/model
+```
+
+**Hitting the API***
+```shell
+curl -k http://localhost:5000/response -H "Content-Type: application/json" -d '{"text": "foobar"}'
+```
+"""
+
+from parlai.core.agents import create_agent
+from parlai.core.params import ParlaiParser
+from parlai.core.script import ParlaiScript, register_script
+
+
+@register_script('flask', hidden=True)
+class Flask(ParlaiScript):
+    @classmethod
+    def setup_args(cls):
+        parser = ParlaiParser(True, True)
+        return parser
+
+    def chatbot_response(self):
+        from flask import request
+
+        data = request.json
+        self.agent.observe({'text': data["text"], 'episode_done': False})
+        response = self.agent.act()
+        return {'response': response['text']}
+
+    def run(self):
+        from flask import Flask
+
+        self.agent = create_agent(self.opt)
+        app = Flask("parlai_flask")
+        app.route("/response", methods=("GET", "POST"))(self.chatbot_response)
+        app.run()
+
+
+if __name__ == "__main__":
+    Flask.main()