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Async http client/server framework (asyncio)

Project description

Async http client/server framework

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aiohttp 2.0 release!

For this release we completely refactored low-level implementation of http handling. Finally uvloop gives performance improvement. Overall performance improvement should be around 70-90% compared to 1.x version.

We took opportunity to refactor long standing api design problems across whole package. Client exceptions handling has been cleaned up and now much more straight forward. Client payload management simplified and allows to extend with any custom type. Client connection pool implementation has been redesigned as well, now there is no need for actively releasing response objects, aiohttp handles connection release automatically.

Another major change, we moved aiohttp development to public organization

With this amount of api changes we had to make backward incompatible changes. Please check this migration document

Please report problems or annoyance with with api to


  • Supports both client and server side of HTTP protocol.

  • Supports both client and server Web-Sockets out-of-the-box.

  • Web-server has middlewares and pluggable routing.

Getting started


To retrieve something from the web:

import aiohttp
import asyncio
import async_timeout

async def fetch(session, url):
    with async_timeout.timeout(10):
        async with session.get(url) as response:
            return await response.text()

async def main():
    async with aiohttp.ClientSession() as session:
        html = await fetch(session, '')

if __name__ == '__main__':
    loop = asyncio.get_event_loop()


This is simple usage example:

from aiohttp import web

async def handle(request):
    name = request.match_info.get('name', "Anonymous")
    text = "Hello, " + name
    return web.Response(text=text)

async def wshandler(request):
    ws = web.WebSocketResponse()
    await ws.prepare(request)

    async for msg in ws:
        if msg.type == web.MsgType.text:
            await ws.send_str("Hello, {}".format(
        elif msg.type == web.MsgType.binary:
            await ws.send_bytes(
        elif msg.type == web.MsgType.close:

    return ws

app = web.Application()
app.router.add_get('/echo', wshandler)
app.router.add_get('/', handle)
app.router.add_get('/{name}', handle)


Note: examples are written for Python 3.5+ and utilize PEP-492 aka async/await. If you are using Python 3.4 please replace await with yield from and async def with @coroutine e.g.:

async def coro(...):
    ret = await f()

should be replaced by:

def coro(...):
    ret = yield from f()


Communication channels

aio-libs google group:!forum/aio-libs

Feel free to post your questions and ideas here.

gitter chat

We support Stack Overflow. Please add aiohttp tag to your question there.


Optionally you may install the cChardet and aiodns libraries (highly recommended for sake of speed).


aiohttp is offered under the Apache 2 license.


The aiohttp community would like to thank Keepsafe ( for it’s support in the early days of the project.

Source code

The latest developer version is available in a github repository:


If you are interested in by efficiency, AsyncIO community maintains a list of benchmarks on the official wiki:


2.2.5 (2017-08-03)

  • Don’t raise deprecation warning on loop.run_until_complete(client.close()) (#2065)

2.2.4 (2017-08-02)

  • Fix issue with synchronous session closing when using ClientSession as an asynchronous context manager. (#2063)

2.2.3 (2017-07-04)

  • Fix _CoroGuard for python 3.4

2.2.2 (2017-07-03)

  • Allow await session.close() along with yield from session.close()

2.2.1 (2017-07-02)

  • Relax yarl requirement to 0.11+

  • Backport #2026: session.close is a coroutine (#2029)

2.2.0 (2017-06-20)

  • Add doc for add_head, update doc for add_get. (#1944)

  • Fixed consecutive calls for Response.write_eof.

  • Retain method attributes (e.g. __doc__) when registering synchronous handlers for resources. (#1953)

  • Added signal TERM handling in run_app to gracefully exit (#1932)

  • Fix websocket issues caused by frame fragmentation. (#1962)

  • Raise RuntimeError is you try to set the Content Length and enable chunked encoding at the same time (#1941)

  • Small update for unittest_run_loop

  • Use CIMultiDict for ClientRequest.skip_auto_headers (#1970)

  • Fix wrong startup sequence: test server and run_app() are not raise DeprecationWarning now (#1947)

  • Make sure cleanup signal is sent if startup signal has been sent (#1959)

  • Fixed server keep-alive handler, could cause 100% cpu utilization (#1955)

  • Connection can be destroyed before response get processed if await aiohttp.request(..) is used (#1981)

  • MultipartReader does not work with -OO (#1969)

  • Fixed ClientPayloadError with blank Content-Encoding header (#1931)

  • Support deflate encoding implemented in (#1918)

  • Fix BadStatusLine caused by extra CRLF after POST data (#1792)

  • Keep a reference to ClientSession in response object (#1985)

  • Deprecate undocumented app.on_loop_available signal (#1978)

2.1.0 (2017-05-26)

  • Added support for experimental async-tokio event loop written in Rust

  • Write to transport \r\n before closing after keepalive timeout, otherwise client can not detect socket disconnection. (#1883)

  • Only call loop.close in run_app if the user did not supply a loop. Useful for allowing clients to specify their own cleanup before closing the asyncio loop if they wish to tightly control loop behavior

  • Content disposition with semicolon in filename (#917)

  • Added request_info to response object and ClientResponseError. (#1733)

  • Added history to ClientResponseError. (#1741)

  • Allow to disable redirect url re-quoting (#1474)

  • Handle RuntimeError from transport (#1790)

  • Dropped “%O” in access logger (#1673)

  • Added args and kwargs to unittest_run_loop. Useful with other decorators, for example @patch. (#1803)

  • Added iter_chunks to response.content object. (#1805)

  • Avoid creating TimerContext when there is no timeout to allow compatibility with Tornado. (#1817) (#1180)

  • Add proxy_from_env to ClientRequest to read from environment variables. (#1791)

  • Add DummyCookieJar helper. (#1830)

  • Fix assertion errors in Python 3.4 from noop helper. (#1847)

  • Do not unquote + in match_info values (#1816)

  • Use Forwarded, X-Forwarded-Scheme and X-Forwarded-Host for better scheme and host resolution. (#1134)

  • Fix sub-application middlewares resolution order (#1853)

  • Fix applications comparison (#1866)

  • Fix static location in index when prefix is used (#1662)

  • Make test server more reliable (#1896)

  • Extend list of web exceptions, add HTTPUnprocessableEntity, HTTPFailedDependency, HTTPInsufficientStorage status codes (#1920)

2.0.7 (2017-04-12)

  • Fix pypi distribution

  • Fix exception description (#1807)

  • Handle socket error in FileResponse (#1773)

  • Cancel websocket heartbeat on close (#1793)

2.0.6 (2017-04-04)

  • Keeping blank values for and multipart.form() (#1765)

  • TypeError in data_received of ResponseHandler (#1770)

  • Fix web.run_app not to bind to default host-port pair if only socket is passed (#1786)

2.0.5 (2017-03-29)

  • Memory leak with aiohttp.request (#1756)

  • Disable cleanup closed ssl transports by default.

  • Exception in request handling if the server responds before the body is sent (#1761)

2.0.4 (2017-03-27)

  • Memory leak with aiohttp.request (#1756)

  • Encoding is always UTF-8 in POST data (#1750)

  • Do not add “Content-Disposition” header by default (#1755)

2.0.3 (2017-03-24)

  • Call https website through proxy will cause error (#1745)

  • Fix exception on multipart/form-data post if content-type is not set (#1743)

2.0.2 (2017-03-21)

  • Fixed Application.on_loop_available signal (#1739)

  • Remove debug code

2.0.1 (2017-03-21)

  • Fix allow-head to include name on route (#1737)

  • Fixed AttributeError in WebSocketResponse.can_prepare (#1736)

2.0.0 (2017-03-20)

  • Added json to ClientSession.request() method (#1726)

  • Added session’s raise_for_status parameter, automatically calls raise_for_status() on any request. (#1724)

  • response.json() raises ClientReponseError exception if response’s content type does not match (#1723)

    • Cleanup timer and loop handle on any client exception.

  • Deprecate loop parameter for Application’s constructor

2.0.0rc1 (2017-03-15)

  • Properly handle payload errors (#1710)

  • Added ClientWebSocketResponse.get_extra_info() (#1717)

  • It is not possible to combine Transfer-Encoding and chunked parameter, same for compress and Content-Encoding (#1655)

  • Connector’s limit parameter indicates total concurrent connections. New limit_per_host added, indicates total connections per endpoint. (#1601)

  • Use url’s raw_host for name resolution (#1685)

  • Change ClientResponse.url to yarl.URL instance (#1654)

  • Add max_size parameter to web.Request reading methods (#1133)

  • Web stores data in temp files (#1469)

  • Add the allow_head=True keyword argument for add_get (#1618)

  • run_app and the Command Line Interface now support serving over Unix domain sockets for faster inter-process communication.

  • run_app now supports passing a preexisting socket object. This can be useful e.g. for socket-based activated applications, when binding of a socket is done by the parent process.

  • Implementation for Trailer headers parser is broken (#1619)

  • Fix FileResponse to not fall on bad request (range out of file size)

  • Fix FileResponse to correct stream video to Chromes

  • Deprecate public low-level api (#1657)

  • Deprecate encoding parameter for ClientSession.request() method

  • Dropped aiohttp.wsgi (#1108)

  • Dropped version from ClientSession.request() method

  • Dropped websocket version 76 support (#1160)

  • Dropped: aiohttp.protocol.HttpPrefixParser (#1590)

  • Dropped: Servers response’s .started, .start() and .can_start() method (#1591)

  • Dropped: Adding sub app via app.router.add_subapp() is deprecated use app.add_subapp() instead (#1592)

  • Dropped: Application.finish() and Application.register_on_finish() (#1602)

  • Dropped: web.Request.GET and web.Request.POST

  • Dropped: aiohttp.get(), aiohttp.options(), aiohttp.head(),, aiohttp.put(), aiohttp.patch(), aiohttp.delete(), and aiohttp.ws_connect() (#1593)

  • Dropped: aiohttp.web.WebSocketResponse.receive_msg() (#1605)

  • Dropped: ServerHttpProtocol.keep_alive_timeout attribute and keep-alive, keep_alive_on, timeout, log constructor parameters (#1606)

  • Dropped: TCPConnector’s` .resolve, .resolved_hosts, .clear_resolved_hosts() attributes and resolve constructor parameter (#1607)

  • Dropped ProxyConnector (#1609)

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