Aiohttp tutorial

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:

You can find complete project on the Github.

What are we going to build?

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

We will build a REST API application that searches for funny GIFs on the Giphy. 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:

{
    "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:

mkdir giphynav-aiohttp-tutorial
cd giphynav-aiohttp-tutorial

Now let’s create and activate virtual environment:

python3 -m venv venv
. 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
│   └── handlers.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:

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

and run next in the terminal:

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:

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 will answer our requests in json format. There will be no payload for now.

Edit handlers.py:

"""Handlers 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 a container. Container will keep all of the application components and their dependencies.

Edit containers.py:

"""Containers module."""

from dependency_injector import containers


class Container(containers.DeclarativeContainer):
    ...

Container is empty for now. We will add the providers in the following sections.

Finally we need to create aiohttp application factory. It will create and configure container and web.Application. It is traditionally called create_app(). We will assign index handler to handle user requests to the root / of our web application.

Put next into the application.py:

"""Application module."""

from aiohttp import web

from .containers import Container
from . import handlers


def create_app() -> web.Application:
    container = Container()

    app = web.Application()
    app.container = container
    app.add_routes([
        web.get('/', handlers.index),
    ])
    return app

Now we’re ready to run our application

Do next in the terminal:

adev runserver giphynavigator/application.py --livereload

The output should be something like:

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

Let’s check that it works. Open another terminal session and use httpie:

http http://127.0.0.1:8000/

You should see:

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:

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

and put next into it:

"""Giphy client module."""

from aiohttp import ClientSession, ClientTimeout


class GiphyClient:

    API_URL = 'https://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:

"""Containers module."""

from dependency_injector import containers, providers

from . import giphy


class Container(containers.DeclarativeContainer):

    config = providers.Configuration()

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

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:

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

and put next into it:

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:

"""Application module."""

from aiohttp import web

from .containers import Container
from . import handlers


def create_app() -> web.Application:
    container = Container()
    container.config.from_yaml('config.yml')
    container.config.giphy.api_key.from_env('GIPHY_API_KEY')

    app = web.Application()
    app.container = container
    app.add_routes([
        web.get('/', handlers.index),
    ])
    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:

export GIPHY_API_KEY=wBJ2wZG7SRqfrU9nPgPiWvORmloDyuL0

Note

To create your own Giphy API key follow this guide.

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:

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

and put next into it:

"""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 when we add SearchService to the container.

Edit containers.py:

"""Containers module."""

from dependency_injector import containers, providers

from . import giphy, services


class Container(containers.DeclarativeContainer):

    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,
    )

The search service is ready. In next section we’re going to put it to work.

Make the search work

Now we are ready to put the search into work. Let’s inject SearchService into the index handler. We will use Wiring feature.

Edit handlers.py:

"""Handlers module."""

from aiohttp import web
from dependency_injector.wiring import Provide

from .services import SearchService
from .containers import Container


async def index(
        request: web.Request,
        search_service: SearchService = Provide[Container.search_service],
) -> 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,
        },
    )

To make the injection work we need to wire the container instance with the handlers module. This needs to be done once. After it’s done we can use Provide markers to specify as many injections as needed for any handler.

Edit application.py:

"""Application module."""

from aiohttp import web

from .containers import Container
from . import handlers


def create_app() -> web.Application:
    container = Container()
    container.config.from_yaml('config.yml')
    container.config.giphy.api_key.from_env('GIPHY_API_KEY')
    container.wire(modules=[handlers])

    app = web.Application()
    app.container = container
    app.add_routes([
        web.get('/', handlers.index),
    ])
    return app

Make sure the app is running or use:

adev runserver giphynavigator/application.py --livereload

and make a request to the API in the terminal:

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

You should see:

HTTP/1.1 200 OK
Content-Length: 492
Content-Type: application/json; charset=utf-8
Date: Fri, 09 Oct 2020 01:35:48 GMT
Server: Python/3.8 aiohttp/3.6.2

{
    "gifs": [
        {
            "url": "https://giphy.com/gifs/dollyparton-3xIVVMnZfG3KQ9v4Ye"
        },
        {
            "url": "https://giphy.com/gifs/tennistv-unbelievable-disbelief-cant-believe-UWWJnhHHbpGvZOapEh"
        },
        {
            "url": "https://giphy.com/gifs/discoverychannel-nugget-gold-rush-rick-ness-KGGPIlnC4hr4u2s3pY"
        },
        {
            "url": "https://giphy.com/gifs/soulpancake-wow-work-xUe4HVXTPi0wQ2OAJC"
        },
        {
            "url": "https://giphy.com/gifs/readingrainbow-teamwork-levar-burton-reading-rainbow-3o7qE1EaTWLQGDSabK"
        }
    ],
    "limit": 5,
    "query": "wow,it works"
}
https://media.giphy.com/media/3oxHQCI8tKXoeW4IBq/source.gif

The search works!

Make some refactoring

Our index handler 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 handlers.py:

"""Handlers module."""

from aiohttp import web
from dependency_injector.wiring import Provide

from .services import SearchService
from .containers import Container


async def index(
        request: web.Request,
        search_service: SearchService = Provide[Container.search_service],
        default_query: str = Provide[Container.config.default.query],
        default_limit: int = Provide[Container.config.default.limit.as_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,
        },
    )

Let’s update the config.

Edit config.yml:

giphy:
  request_timeout: 10
default:
  query: "Dependency Injector"
  limit: 10

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

Tests

In this section we will add some tests.

Create tests.py module in the giphynavigator package:

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

and put next into it:

"""Tests module."""

from unittest import mock

import pytest

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


@pytest.fixture
def app():
    app = create_app()
    yield app
    app.container.unwire()


@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.default.query()
    assert data['limit'] == app.container.config.default.limit()

Now let’s run it and check the coverage:

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

You should see:

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.

Containers and Providers helped to specify how to assemble search service and giphy client.

Configuration provider helped to deal with reading YAML file and environment variable.

We used Wiring feature to inject the dependencies into the index() handler. Provider overriding feature helped in testing.

We kept all the dependencies injected explicitly. This will help when you need to add or change something in future.

You can find complete project on the Github.

What’s next?