aiohttp is HTTP client/server for python and AsyncIO. It supports both server websockets and client websockets. As it works asynchronously, it can handle hundreds of requests per seconds providing better performance than other frameworks.
AsyncIO is a python library for writing:
Single-threaded concurrent code using coroutines.
Multiplexing I/O access over sockets and other resources.
Running network clients and servers, and other related primitives.
This provides concurrency especially for I/O bound tasks over sockets and other resources. Concurrency ensures that user does not have wait for the I/O bound results.
In this article, we will create a rest API for our application using aiohttp. It is a simple application which has a Note table.
Set up aiohttp
Activate a virtual environment in python 3 and install aiohttp
pip install aiohttp
or clone the github repository and install the requirements
pip install -r requirements.txt
Create Models
We will configure application to use sqlite as our database in models.py
# DBSession = scoped_session(sessionmaker(extension=ZopeTransactionExtension()))
DB_URI = 'sqlite:///stuff.db'
Session = sessionmaker(autocommit=False,
autoflush=False,
bind=create_engine(DB_URI))
session = scoped_session(Session)
Base = declarative_base()
Then we create Note class for note objects in models.py
class Note(Base):
__tablename__ = 'notes'
id = Column(Integer, primary_key=True)
title = Column(String(50))
description = Column(String(50))
created_at = Column(String(50))
created_by = Column(String(50))
priority = Column(Integer)
def __init__(self, title, description, created_at ,created_by, priority):
self.title = title
self.description = description
self.created_at = created_at
self.created_by = created_by
self.priority = priority
@classmethod
def from_json(cls, data):
return cls(**data)
def to_json(self):
to_serialize = ['id', 'title', 'description', 'created_at', 'created_by', 'priority']
d = {}
for attr_name in to_serialize:
d[attr_name] = getattr(self, attr_name)
return d
Resources
We define our API endpoints in aiohttp_rest.py file.
DEFAULT_METHODS = ('GET', 'POST', 'PUT', 'DELETE')
class RestEndpoint:
def __init__(self):
self.methods = {}
for method_name in DEFAULT_METHODS:
method = getattr(self, method_name.lower(), None)
if method:
self.register_method(method_name, method)
def register_method(self, method_name, method):
self.methods[method_name.upper()] = method
async def dispatch(self, request: Request):
method = self.methods.get(request.method.upper())
if not method:
raise HTTPMethodNotAllowed('', DEFAULT_METHODS)
wanted_args = list(inspect.signature(method).parameters.keys())
available_args = request.match_info.copy()
available_args.update({'request': request})
unsatisfied_args = set(wanted_args) - set(available_args.keys())
if unsatisfied_args:
# Expected match info that doesn't exist
raise HttpBadRequest('')
return await method(**{arg_name: available_args[arg_name] for arg_name in wanted_args})
class CollectionEndpoint(RestEndpoint):
def __init__(self, resource):
super().__init__()
self.resource = resource
async def get(self) -> Response:
data = []
notes = session.query(Note).all()
for instance in self.resource.collection.values():
data.append(self.resource.render(instance))
data = self.resource.encode(data)
return Response ( status=200, body=self.resource.encode({
'notes': [
{'id': note.id, 'title': note.title, 'description': note.description,
'created_at': note.created_at, 'created_by': note.created_by, 'priority': note.priority}
for note in session.query(Note)
]
}), content_type='application/json')
async def post(self, request):
data = await request.json()
note=Note(title=data['title'], description=data['description'], created_at=data['created_at'], created_by=data['created_by'], priority=data['priority'])
session.add(note)
session.commit()
return Response(status=201, body=self.resource.encode({
'notes': [
{'id': note.id, 'title': note.title, 'description': note.description,
'created_at': note.created_at, 'created_by': note.created_by, 'priority': note.priority}
for note in session.query(Note)
]
}), content_type='application/json')
class InstanceEndpoint(RestEndpoint):
def __init__(self, resource):
super().__init__()
self.resource = resource
async def get(self, instance_id):
instance = session.query(Note).filter(Note.id == instance_id).first()
if not instance:
return Response(status=404, body=json.dumps({'not found': 404}), content_type='application/json')
data = self.resource.render_and_encode(instance)
return Response(status=200, body=data, content_type='application/json')
async def put(self, request, instance_id):
data = await request.json()
note = session.query(Note).filter(Note.id == instance_id).first()
note.title = data['title']
note.description = data['description']
note.created_at = data['created_at']
note.created_by = data['created_by']
note.priority = data['priority']
session.add(note)
session.commit()
return Response(status=201, body=self.resource.render_and_encode(note),
content_type='application/json')
async def delete(self, instance_id):
note = session.query(Note).filter(Note.id == instance_id).first()
if not note:
abort(404, message="Note {} doesn't exist".format(id))
session.delete(note)
session.commit()
return Response(status=204)
class RestResource:
def __init__(self, notes, factory, collection, properties, id_field):
self.notes = notes
self.factory = factory
self.collection = collection
self.properties = properties
self.id_field = id_field
self.collection_endpoint = CollectionEndpoint(self)
self.instance_endpoint = InstanceEndpoint(self)
def register(self, router: UrlDispatcher):
router.add_route('*', '/{notes}'.format(notes=self.notes), self.collection_endpoint.dispatch)
router.add_route('*', '/{notes}/{{instance_id}}'.format(notes=self.notes), self.instance_endpoint.dispatch)
def render(self, instance):
return OrderedDict((notes, getattr(instance, notes)) for notes in self.properties)
@staticmethod
def encode(data):
return json.dumps(data, indent=4).encode('utf-8')
def render_and_encode(self, instance):
return self.encode(self.render(instance))
By using async keyword with all methods (GET, POST, PUT and DELETE), we ensure that those operations are performed asynchronously and the response is returned from from both collection end point and instance end points. After setting up our endpoints, we declare resources in aio-app.py file.
from aiohttp.web import Application, run_app
from aiohttp_rest import RestResource
from models import Note
from sqlalchemy import engine_from_config
notes = {}
app = Application()
person_resource = RestResource('notes', Note, notes, ('title', 'description', 'created_at', 'created_by', 'priority'), 'title')
person_resource.register(app.router)
if __name__ == '__main__':
run_app(app)
Running the application
First create the database by:
python models.py
Run the app by executing following in terminal
python aio-app.py
Open python shell and execute some requests
requests.post('http://localhost:8080/notes',
data=json.dumps({ "title": "note two",
"created_at": "2017-08-23 00:00", "created_by": "apcelent", "description": "sample notes", "priority": 4
}))
requests.put('http://localhost:8080/notes/1',
data=json.dumps({ "title": "note edit",
"created_at": "2017-08-23 00:00", "created_by": "apcelent", "description": "sample notes edit", "priority": 4
}))
requests.delete('http://localhost:8080/notes/1')
These will create some notes in database using aiohttp REST API. These notes can be viewed at http://127.0.0.1:8080/notes
The source code can be found here.
The article originally appeared on Apcelent Tech Blog.
Top comments (2)
Hello, how are you @apcelent ?
There's an issue about the way you wrote this API.
SQLAlchemy is not asyncio aware. This means that all the query listed above will make the python thread idle leading to inefficient I/O and scaling to one coroutine per thread. I strongly recommend a review of python asyncio model.
If you want use sqlAlchemy an alternative is here github.com/RazerM/sqlalchemy_aio.
Otherwise, is better get back to flask and use gevent to enable concurrent async I/O.
This tutorial is broken.