.. _aiohttp-tutorial:

Aiohttp tutorial
================

.. meta::
   :keywords: Python,Aiohttp,Tutorial,Education,Web,API,REST API,Example,DI,Dependency injection,
              IoC,Inversion of control,Refactoring,Tests,Unit tests,Pytest,py.test,Bootstrap,
              HTML,CSS
   :description: This tutorial shows how to build an aiohttp application following the dependency
                 injection principle. You will create the REST API application, connect to the
                 Giphy API, cover it with the unit test and make some refactoring.

This tutorial shows how to build an ``aiohttp`` REST API application following the dependency
injection principle.

Start from the scratch or jump to the section:

.. contents::
   :local:
   :backlinks: none

You can find complete project on the
`Github <https://github.com/ets-labs/python-dependency-injector/tree/master/examples/miniapps/giphynav-aiohttp>`_.

What are we going to build?
---------------------------

.. image:: https://media.giphy.com/media/apvx5lPCPsjN6/source.gif

We will build a REST API application that searches for funny GIFs on the `Giphy <https://giphy.com/>`_.
Let's call it Giphy Navigator.

How does Giphy Navigator work?

- Client sends a request specifying the search query and the number of results.
- Giphy Navigator returns a response in json format.
- The response contains:
    - the search query
    - the limit number
    - the list of gif urls

Example response:

.. code-block:: json

   {
       "query": "Dependency Injector",
       "limit": 10,
       "gifs": [
           {
               "url": "https://giphy.com/gifs/boxes-dependent-swbf2-6Eo7KzABxgJMY"
           },
           {
               "url": "https://giphy.com/gifs/depends-J56qCcOhk6hKE"
           },
           {
               "url": "https://giphy.com/gifs/web-series-ccstudios-bro-dependent-1lhU8KAVwmVVu"
           },
           {
               "url": "https://giphy.com/gifs/TheBoysTV-friends-friend-weneedeachother-XxR9qcIwcf5Jq404Sx"
           },
           {
               "url": "https://giphy.com/gifs/netflix-a-series-of-unfortunate-events-asoue-9rgeQXbwoK53pcxn7f"
           },
           {
               "url": "https://giphy.com/gifs/black-and-white-sad-skins-Hs4YzLs2zJuLu"
           },
           {
               "url": "https://giphy.com/gifs/always-there-for-you-i-am-here-PlayjhCco9jHBYrd9w"
           },
           {
               "url": "https://giphy.com/gifs/stream-famous-dollar-YT2dvOByEwXCdoYiA1"
           },
           {
               "url": "https://giphy.com/gifs/i-love-you-there-for-am-1BhGzgpZXYWwWMAGB1"
           },
           {
               "url": "https://giphy.com/gifs/life-like-twerk-9hlnWxjHqmH28"
           }
       ]
   }

The task is naive and that's exactly what we need for the tutorial.

Prepare the environment
-----------------------

Let's create the environment for the project.

First we need to create a project folder and the virtual environment:

.. code-block:: bash

   mkdir giphynav-aiohttp-tutorial
   cd giphynav-aiohttp-tutorial
   python3 -m venv venv

Now let's activate the virtual environment:

.. code-block:: bash

   . venv/bin/activate

Environment is ready and now we're going to create the layout of the project.

Project layout
--------------

Create next structure in the current directory. All files should be empty. That's ok for now.

Initial project layout::

   ./
   ├── giphynavigator/
   │   ├── __init__.py
   │   ├── application.py
   │   ├── containers.py
   │   └── views.py
   ├── venv/
   └── requirements.txt

Install the requirements
------------------------

Now it's time to install the project requirements. We will use next packages:

- ``dependency-injector`` - the dependency injection framework
- ``aiohttp`` - the web framework
- ``aiohttp-devtools`` - the helper library that will provide a development server with live
  reloading
- ``pyyaml`` - the YAML files parsing library, used for the reading of the configuration files
- ``pytest-aiohttp`` - the helper library for the testing of the ``aiohttp`` application
- ``pytest-cov`` - the helper library for measuring the test coverage

Put next lines into the ``requirements.txt`` file:

.. code-block:: bash

   dependency-injector
   aiohttp
   aiohttp-devtools
   pyyaml
   pytest-aiohttp
   pytest-cov

and run next in the terminal:

.. code-block:: bash

   pip install -r requirements.txt

Let's also install the ``httpie``. It is a user-friendly command-line HTTP client for the API era.
We will use it for the manual testing.

Run the command in the terminal:

.. code-block:: bash

   pip install httpie

The requirements are setup. Now we will build a minimal application.

Minimal application
-------------------

In this section we will build a minimal application. It will have an endpoint that we can call.
The endpoint will answer in the right format and will have no data.

Edit ``views.py``:

.. code-block:: python

   """Views module."""

   from aiohttp import web


   async def index(request: web.Request) -> web.Response:
       query = request.query.get('query', 'Dependency Injector')
       limit = int(request.query.get('limit', 10))

       gifs = []

       return web.json_response(
           {
               'query': query,
               'limit': limit,
               'gifs': gifs,
           },
       )

Now let's create the main part of our application - the container. Container will keep all of the
application components and their dependencies. First two providers we need to add are
the ``aiohttp`` application provider and the view provider.

Put next into the ``containers.py``:

.. code-block:: python

   """Application containers module."""

   from dependency_injector import containers
   from dependency_injector.ext import aiohttp
   from aiohttp import web

   from . import views


   class ApplicationContainer(containers.DeclarativeContainer):
       """Application container."""

       app = aiohttp.Application(web.Application)

       index_view = aiohttp.View(views.index)

At the last we need to create the ``aiohttp`` application factory. It is traditionally called
``create_app()``. It will create the container. Then it will use the container to create
the ``aiohttp`` application. Last step is to configure the routing - we will assign
``index_view`` from the container to handle the requests to the root ``/`` of our REST API server.

Put next into the ``application.py``:

.. code-block:: python

   """Application module."""

   from aiohttp import web

   from .containers import ApplicationContainer


   def create_app():
       """Create and return aiohttp application."""
       container = ApplicationContainer()

       app: web.Application = container.app()
       app.container = container

       app.add_routes([
           web.get('/', container.index_view.as_view()),
       ])

       return app

.. note::

   Container is the first object in the application.

   The container is used to create all other objects.

Now we're ready to run our application

Do next in the terminal:

.. code-block:: bash

   adev runserver giphynavigator/application.py --livereload

The output should be something like:

.. code-block:: bash

   [18:52:59] Starting aux server at http://localhost:8001 ◆
   [18:52:59] Starting dev server at http://localhost:8000 ●

Let's use ``httpie`` to check that it works:

.. code-block:: bash

   http http://127.0.0.1:8000/

You should see:

.. code-block:: json

   HTTP/1.1 200 OK
   Content-Length: 844
   Content-Type: application/json; charset=utf-8
   Date: Wed, 29 Jul 2020 21:01:50 GMT
   Server: Python/3.8 aiohttp/3.6.2

   {
       "gifs": [],
       "limit": 10,
       "query": "Dependency Injector"
   }

Minimal application is ready. Let's connect our application with the Giphy API.

Giphy API client
----------------

In this section we will integrate our application with the Giphy API.

We will create our own API client using ``aiohttp`` client.

Create ``giphy.py`` module in the ``giphynavigator`` package:

.. code-block:: bash
   :emphasize-lines: 6

   ./
   ├── giphynavigator/
   │   ├── __init__.py
   │   ├── application.py
   │   ├── containers.py
   │   ├── giphy.py
   │   └── views.py
   ├── venv/
   └── requirements.txt

and put next into it:

.. code-block:: python

   """Giphy client module."""

   from aiohttp import ClientSession, ClientTimeout


   class GiphyClient:

       API_URL = 'http://api.giphy.com/v1'

       def __init__(self, api_key, timeout):
           self._api_key = api_key
           self._timeout = ClientTimeout(timeout)

       async def search(self, query, limit):
           """Make search API call and return result."""
           url = f'{self.API_URL}/gifs/search'
           params = {
               'q': query,
               'api_key': self._api_key,
               'limit': limit,
           }
           async with ClientSession(timeout=self._timeout) as session:
               async with session.get(url, params=params) as response:
                   if response.status != 200:
                       response.raise_for_status()
                   return await response.json()

Now we need to add ``GiphyClient`` into the container. The ``GiphyClient`` has two dependencies
that have to be injected: the API key and the request timeout. We will need to use two more
providers from the ``dependency_injector.providers`` module:

- ``Factory`` provider that will create the ``GiphyClient`` client.
- ``Configuration`` provider that will provide the API key and the request timeout.

Edit ``containers.py``:

.. code-block:: python
   :emphasize-lines: 3,7,15,17-21

   """Application containers module."""

   from dependency_injector import containers, providers
   from dependency_injector.ext import aiohttp
   from aiohttp import web

   from . import giphy, views


   class ApplicationContainer(containers.DeclarativeContainer):
       """Application container."""

       app = aiohttp.Application(web.Application)

       config = providers.Configuration()

       giphy_client = providers.Factory(
           giphy.GiphyClient,
           api_key=config.giphy.api_key,
           timeout=config.giphy.request_timeout,
       )

       index_view = aiohttp.View(views.index)

.. note::

   We have used the configuration value before it was defined. That's the principle how the
   ``Configuration`` provider works.

   Use first, define later.

Now let's add the configuration file.

We will use YAML.

Create an empty file ``config.yml`` in the root root of the project:

.. code-block:: bash
   :emphasize-lines: 9

   ./
   ├── giphynavigator/
   │   ├── __init__.py
   │   ├── application.py
   │   ├── containers.py
   │   ├── giphy.py
   │   └── views.py
   ├── venv/
   ├── config.yml
   └── requirements.txt

and put next into it:

.. code-block:: yaml

   giphy:
     request_timeout: 10

We will use an environment variable ``GIPHY_API_KEY`` to provide the API key.

Now we need to edit ``create_app()`` to make two things when application starts:

- Load the configuration file the ``config.yml``.
- Load the API key from the ``GIPHY_API_KEY`` environment variable.

Edit ``application.py``:

.. code-block:: python
   :emphasize-lines: 11-12

   """Application module."""

   from aiohttp import web

   from .containers import ApplicationContainer


   def create_app():
       """Create and return aiohttp application."""
       container = ApplicationContainer()
       container.config.from_yaml('config.yml')
       container.config.giphy.api_key.from_env('GIPHY_API_KEY')

       app: web.Application = container.app()
       app.container = container

       app.add_routes([
           web.get('/', container.index_view.as_view()),
       ])

       return app

Now we need to create an API key and set it to the environment variable.

As for now, don’t worry, just take this one:

.. code-block:: bash

   export GIPHY_API_KEY=wBJ2wZG7SRqfrU9nPgPiWvORmloDyuL0

.. note::

   To create your own Giphy API key follow this
   `guide <https://support.giphy.com/hc/en-us/articles/360020283431-Request-A-GIPHY-API-Key>`_.

The Giphy API client and the configuration setup is done. Let's proceed to the search service.

Search service
--------------

Now it's time to add the ``SearchService``. It will:

- Perform the search.
- Format result data.

``SearchService`` will use ``GiphyClient``.

Create ``services.py`` module in the ``giphynavigator`` package:

.. code-block:: bash
   :emphasize-lines: 7

   ./
   ├── giphynavigator/
   │   ├── __init__.py
   │   ├── application.py
   │   ├── containers.py
   │   ├── giphy.py
   │   ├── services.py
   │   └── views.py
   ├── venv/
   └── requirements.txt

and put next into it:

.. code-block:: python

   """Services module."""

   from .giphy import GiphyClient


   class SearchService:

       def __init__(self, giphy_client: GiphyClient):
           self._giphy_client = giphy_client

       async def search(self, query, limit):
           """Search for gifs and return formatted data."""
           if not query:
               return []

           result = await self._giphy_client.search(query, limit)

           return [{'url': gif['url']} for gif in result['data']]

The ``SearchService`` has a dependency on the ``GiphyClient``. This dependency will be injected.
Let's add ``SearchService`` to the container.

Edit ``containers.py``:

.. code-block:: python
   :emphasize-lines: 7,23-26

   """Application containers module."""

   from dependency_injector import containers, providers
   from dependency_injector.ext import aiohttp
   from aiohttp import web

   from . import giphy, services, views


   class ApplicationContainer(containers.DeclarativeContainer):
       """Application container."""

       app = aiohttp.Application(web.Application)

       config = providers.Configuration()

       giphy_client = providers.Factory(
           giphy.GiphyClient,
           api_key=config.giphy.api_key,
           timeout=config.giphy.request_timeout,
       )

       search_service = providers.Factory(
           services.SearchService,
           giphy_client=giphy_client,
       )

       index_view = aiohttp.View(views.index)


The search service is ready. In the next section we're going to make it work.

Make the search work
--------------------

Now we are ready to make the search work. Let's use the ``SearchService`` in the ``index`` view.

Edit ``views.py``:

.. code-block:: python
   :emphasize-lines: 5,8-11,15

   """Views module."""

   from aiohttp import web

   from .services import SearchService


   async def index(
           request: web.Request,
           search_service: SearchService,
   ) -> web.Response:
       query = request.query.get('query', 'Dependency Injector')
       limit = int(request.query.get('limit', 10))

       gifs = await search_service.search(query, limit)

       return web.json_response(
           {
               'query': query,
               'limit': limit,
               'gifs': gifs,
           },
       )

Now let's inject the ``SearchService`` dependency into the ``index`` view.

Edit ``containers.py``:

.. code-block:: python
   :emphasize-lines: 28-31

   """Application containers module."""

   from dependency_injector import containers, providers
   from dependency_injector.ext import aiohttp
   from aiohttp import web

   from . import giphy, services, views


   class ApplicationContainer(containers.DeclarativeContainer):
       """Application container."""

       app = aiohttp.Application(web.Application)

       config = providers.Configuration()

       giphy_client = providers.Factory(
           giphy.GiphyClient,
           api_key=config.giphy.api_key,
           timeout=config.giphy.request_timeout,
       )

       search_service = providers.Factory(
           services.SearchService,
           giphy_client=giphy_client,
       )

       index_view = aiohttp.View(
           views.index,
           search_service=search_service,
       )

Make sure the app is running or use:

.. code-block:: bash

   adev runserver giphynavigator/application.py --livereload

and make a request to the API in the terminal:

.. code-block:: bash

   http http://localhost:8000/ query=="wow,it works" limit==5

You should see:

.. code-block:: json

   HTTP/1.1 200 OK
   Content-Length: 850
   Content-Type: application/json; charset=utf-8
   Date: Wed, 29 Jul 2020 22:22:55 GMT
   Server: Python/3.8 aiohttp/3.6.2

   {
       "gifs": [
           {
               "url": "https://giphy.com/gifs/discoverychannel-nugget-gold-rush-rick-ness-KGGPIlnC4hr4u2s3pY"
           },
           {
               "url": "https://giphy.com/gifs/primevideoin-ll1hyBS2IrUPLE0E71"
           },
           {
               "url": "https://giphy.com/gifs/jackman-works-jackmanworks-l4pTgQoCrmXq8Txlu"
           },
           {
               "url": "https://giphy.com/gifs/cat-massage-at-work-l46CzMaOlJXAFuO3u"
           },
           {
               "url": "https://giphy.com/gifs/everwhatproductions-fun-christmas-3oxHQCI8tKXoeW4IBq"
           },
       ],
       "limit": 10,
       "query": "wow,it works"
   }

.. image:: https://media.giphy.com/media/3oxHQCI8tKXoeW4IBq/source.gif

The search works!

Make some refactoring
---------------------

Our ``index`` view has two hardcoded config values:

- Default search query
- Default results limit

Let's make some refactoring. We will move these values to the config.

Edit ``views.py``:

.. code-block:: python
   :emphasize-lines: 11-12,14-15

   """Views module."""

   from aiohttp import web

   from .services import SearchService


   async def index(
           request: web.Request,
           search_service: SearchService,
           default_query: str,
           default_limit: int,
   ) -> web.Response:
       query = request.query.get('query', default_query)
       limit = int(request.query.get('limit', default_limit))

       gifs = await search_service.search(query, limit)

       return web.json_response(
           {
               'query': query,
               'limit': limit,
               'gifs': gifs,
           },
       )

Now we need to inject these values. Let's update the container.

Edit ``containers.py``:

.. code-block:: python
   :emphasize-lines: 31-32

   """Application containers module."""

   from dependency_injector import containers, providers
   from dependency_injector.ext import aiohttp
   from aiohttp import web

   from . import giphy, services, views


   class ApplicationContainer(containers.DeclarativeContainer):
       """Application container."""

       app = aiohttp.Application(web.Application)

       config = providers.Configuration()

       giphy_client = providers.Factory(
           giphy.GiphyClient,
           api_key=config.giphy.api_key,
           timeout=config.giphy.request_timeout,
       )

       search_service = providers.Factory(
           services.SearchService,
           giphy_client=giphy_client,
       )

       index_view = aiohttp.View(
           views.index,
           search_service=search_service,
           default_query=config.search.default_query,
           default_limit=config.search.default_limit,
       )

Finally let's update the config.

Edit ``config.yml``:

.. code-block:: yaml
   :emphasize-lines: 3-5

   giphy:
     request_timeout: 10
   search:
     default_query: "Dependency Injector"
     default_limit: 10

The refactoring is done. We've made it cleaner - hardcoded values are now moved to the config.

In the next section we will add some tests.

Tests
-----

It would be nice to add some tests. Let's do it.

We will use `pytest <https://docs.pytest.org/en/stable/>`_ and
`coverage <https://coverage.readthedocs.io/>`_.

Create ``tests.py`` module in the ``giphynavigator`` package:

.. code-block:: bash
   :emphasize-lines: 8

   ./
   ├── giphynavigator/
   │   ├── __init__.py
   │   ├── application.py
   │   ├── containers.py
   │   ├── giphy.py
   │   ├── services.py
   │   ├── tests.py
   │   └── views.py
   ├── venv/
   └── requirements.txt

and put next into it:

.. code-block:: python
   :emphasize-lines: 30,57,71

   """Tests module."""

   from unittest import mock

   import pytest

   from giphynavigator.application import create_app
   from giphynavigator.giphy import GiphyClient


   @pytest.fixture
   def app():
       return create_app()


   @pytest.fixture
   def client(app, aiohttp_client, loop):
       return loop.run_until_complete(aiohttp_client(app))


   async def test_index(client, app):
       giphy_client_mock = mock.AsyncMock(spec=GiphyClient)
       giphy_client_mock.search.return_value = {
           'data': [
               {'url': 'https://giphy.com/gif1.gif'},
               {'url': 'https://giphy.com/gif2.gif'},
           ],
       }

       with app.container.giphy_client.override(giphy_client_mock):
           response = await client.get(
               '/',
               params={
                   'query': 'test',
                   'limit': 10,
               },
           )

       assert response.status == 200
       data = await response.json()
       assert data == {
           'query': 'test',
           'limit': 10,
           'gifs': [
               {'url': 'https://giphy.com/gif1.gif'},
               {'url': 'https://giphy.com/gif2.gif'},
           ],
       }


   async def test_index_no_data(client, app):
       giphy_client_mock = mock.AsyncMock(spec=GiphyClient)
       giphy_client_mock.search.return_value = {
           'data': [],
       }

       with app.container.giphy_client.override(giphy_client_mock):
           response = await client.get('/')

       assert response.status == 200
       data = await response.json()
       assert data['gifs'] == []


   async def test_index_default_params(client, app):
       giphy_client_mock = mock.AsyncMock(spec=GiphyClient)
       giphy_client_mock.search.return_value = {
           'data': [],
       }

       with app.container.giphy_client.override(giphy_client_mock):
           response = await client.get('/')

       assert response.status == 200
       data = await response.json()
       assert data['query'] == app.container.config.search.default_query()
       assert data['limit'] == app.container.config.search.default_limit()

Now let's run it and check the coverage:

.. code-block:: bash

   py.test giphynavigator/tests.py --cov=giphynavigator

You should see:

.. code-block:: bash

   platform darwin -- Python 3.8.3, pytest-5.4.3, py-1.9.0, pluggy-0.13.1
   plugins: cov-2.10.0, aiohttp-0.3.0, asyncio-0.14.0
   collected 3 items

   giphynavigator/tests.py ...                                     [100%]

   ---------- coverage: platform darwin, python 3.8.3-final-0 -----------
   Name                            Stmts   Miss  Cover
   ---------------------------------------------------
   giphynavigator/__init__.py          0      0   100%
   giphynavigator/__main__.py          5      5     0%
   giphynavigator/application.py      10      0   100%
   giphynavigator/containers.py       10      0   100%
   giphynavigator/giphy.py            14      9    36%
   giphynavigator/services.py          9      1    89%
   giphynavigator/tests.py            35      0   100%
   giphynavigator/views.py             7      0   100%
   ---------------------------------------------------
   TOTAL                              90     15    83%

.. note::

   Take a look at the highlights in the ``tests.py``.

   It emphasizes the overriding of the ``GiphyClient``. The real API call are mocked.

Conclusion
----------

In this tutorial we've built an ``aiohttp`` REST API application following the dependency
injection principle.
We've used the ``Dependency Injector`` as a dependency injection framework.

The benefit you get with the ``Dependency Injector`` is the container. It starts to payoff
when you need to understand or change your application structure. It's easy with the container,
cause you have everything defined explicitly in one place:

.. code-block:: python

   """Application containers module."""

   from dependency_injector import containers, providers
   from dependency_injector.ext import aiohttp
   from aiohttp import web

   from . import giphy, services, views


   class ApplicationContainer(containers.DeclarativeContainer):
       """Application container."""

       app = aiohttp.Application(web.Application)

       config = providers.Configuration()

       giphy_client = providers.Factory(
           giphy.GiphyClient,
           api_key=config.giphy.api_key,
           timeout=config.giphy.request_timeout,
       )

       search_service = providers.Factory(
           services.SearchService,
           giphy_client=giphy_client,
       )

       index_view = aiohttp.View(
           views.index,
           search_service=search_service,
           default_query=config.search.default_query,
           default_limit=config.search.default_limit,
       )

What's next?

- Look at the other :ref:`tutorials`
- Know more about the :ref:`providers`
- Go to the :ref:`contents`

.. disqus::