Client

To get something from the web:

import aiohttp
import asyncio

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

async def main():
    async with aiohttp.ClientSession() as session:
        html = await fetch(session, 'http://python.org')
        print(html)

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

Server

An example using a simple server:

# examples/server_simple.py
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 wshandle(request):
    ws = web.WebSocketResponse()
    await ws.prepare(request)

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

    return ws


app = web.Application()
app.add_routes([web.get('/', handle),
                web.get('/echo', wshandle),
                web.get('/{name}', handle)])

if __name__ == '__main__':
    web.run_app(app)

Features

• Made exceptions pickleable. Also changed the repr of some exceptions. #4077

• Use Iterable type hint instead of Sequence for Application middleware parameter. #4125

Bugfixes

• Reset the sock_read timeout each time data is received for a aiohttp.ClientResponse. #3808

• Fix handling of expired cookies so they are not stored in CookieJar. #4063

• Fix misleading message in the string representation of ClientConnectorError; self.ssl == None means default SSL context, not SSL disabled #4097

• Don’t clobber HTTP status when using FileResponse. #4106

Improved Documentation

• Added minimal required logging configuration to logging documentation. #2469

• Update docs to reflect proxy support. #4100

• Fix typo in code example in testing docs. #4108

Misc

• #4102

Features

• Compatibility with Python 3.8. #4056

Bugfixes

• correct some exception string format #4068

• Emit a warning when ssl.OP_NO_COMPRESSION is unavailable because the runtime is built against an outdated OpenSSL. #4052

• Update multidict requirement to >= 4.5 #4057

Improved Documentation

• Provide pytest-aiohttp namespace for pytest fixtures in docs. #3723

Features

• Add support for Named Pipes (Site and Connector) under Windows. This feature requires Proactor event loop to work. #3629

• Removed Transfer-Encoding: chunked header from websocket responses to be compatible with more http proxy servers. #3798

• Accept non-GET request for starting websocket handshake on server side. #3980

Bugfixes

• Raise a ClientResponseError instead of an AssertionError for a blank HTTP Reason Phrase. #3532

• Fix an issue where cookies would sometimes not be set during a redirect. #3576

• Change normalize_path_middleware to use 308 redirect instead of 301.

  This behavior should prevent clients from being unable to use PUT/POST methods on endpoints that are redirected because of a trailing slash. #3579

• Drop the processed task from all_tasks() list early. It prevents logging about a task with unhandled exception when the server is used in conjunction with asyncio.run(). #3587

• Signal type annotation changed from Signal[Callable[['TraceConfig'], Awaitable[None]]] to Signal[Callable[ClientSession, SimpleNamespace, ...]. #3595

• Use sanitized URL as Location header in redirects #3614

• Improve typing annotations for multipart.py along with changes required by mypy in files that references multipart.py. #3621

• Close session created inside aiohttp.request when unhandled exception occurs #3628

• Cleanup per-chunk data in generic data read. Memory leak fixed. #3631

• Use correct type for add_view and family #3633

• Fix _keepalive field in __slots__ of RequestHandler. #3644

• Properly handle ConnectionResetError, to silence the “Cannot write to closing transport” exception when clients disconnect uncleanly. #3648

• Suppress pytest warnings due to test_utils classes #3660

• Fix overshadowing of overlapped sub-application prefixes. #3701

• Fixed return type annotation for WSMessage.json() #3720

• Properly expose TooManyRedirects publicly as documented. #3818

• Fix missing brackets for IPv6 in proxy CONNECT request #3841

• Make the signature of aiohttp.test_utils.TestClient.request match asyncio.ClientSession.request according to the docs #3852

• Use correct style for re-exported imports, makes mypy --strict mode happy. #3868

• Fixed type annotation for add_view method of UrlDispatcher to accept any subclass of View #3880

• Made cython HTTP parser set Reason-Phrase of the response to an empty string if it is missing. #3906

• Add URL to the string representation of ClientResponseError. #3959

• Accept istr keys in LooseHeaders type hints. #3976

• Fixed race conditions in _resolve_host caching and throttling when tracing is enabled. #4013

• For URLs like “unix://localhost/…” set Host HTTP header to “localhost” instead of “localhost:None”. #4039

Improved Documentation

• Modify documentation for Background Tasks to remove deprecated usage of event loop. #3526

• use if __name__ == '__main__': in server examples. #3775

• Update documentation reference to the default access logger. #3783

• Improve documentation for web.BaseRequest.path and web.BaseRequest.raw_path. #3791

• Removed deprecation warning in tracing example docs #3964

Bugfixes

• Fix stream .read() / .readany() / .iter_any() which used to return a partial content only in case of compressed content #3525

Bugfixes

• Fix type stubs for aiohttp.web.run_app(access_log=True) and fix edge case of access_log=True and the event loop being in debug mode. #3504

• Fix aiohttp.ClientTimeout type annotations to accept None for fields #3511

• Send custom per-request cookies even if session jar is empty #3515

• Restore Linux binary wheels publishing on PyPI

Features

• FileResponse from web_fileresponse.py uses a ThreadPoolExecutor to work with files asynchronously. I/O based payloads from payload.py uses a ThreadPoolExecutor to work with I/O objects asynchronously. #3313

• Internal Server Errors in plain text if the browser does not support HTML. #3483

Bugfixes

• Preserve MultipartWriter parts headers on write. Refactor the way how Payload.headers are handled. Payload instances now always have headers and Content-Type defined. Fix Payload Content-Disposition header reset after initial creation. #3035

• Log suppressed exceptions in GunicornWebWorker. #3464

• Remove wildcard imports. #3468

• Use the same task for app initialization and web server handling in gunicorn workers. It allows to use Python3.7 context vars smoothly. #3471

• Fix handling of chunked+gzipped response when first chunk does not give uncompressed data #3477

• Replace collections.MutableMapping with collections.abc.MutableMapping to avoid a deprecation warning. #3480

• Payload.size type annotation changed from Optional[float] to Optional[int]. #3484

• Ignore done tasks when cancels pending activities on web.run_app finalization. #3497

Improved Documentation

• Add documentation for aiohttp.web.HTTPException. #3490

Misc

• #3487

Features

• The library type annotations are checked in strict mode now.

• Add support for setting cookies for individual request (#2387)

• Application.add_domain implementation (#2809)

• The default app in the request returned by test_utils.make_mocked_request can now have objects assigned to it and retrieved using the [] operator. (#3174)

• Make request.url accessible when transport is closed. (#3177)

• Add zlib_executor_size argument to Response constructor to allow compression to run in a background executor to avoid blocking the main thread and potentially triggering health check failures. (#3205)

• Enable users to set ClientTimeout in aiohttp.request (#3213)

• Don’t raise a warning if NETRC environment variable is not set and ~/.netrc file doesn’t exist. (#3267)

• Add default logging handler to web.run_app If the Application.debug` flag is set and the default logger aiohttp.access is used, access logs will now be output using a stderr StreamHandler if no handlers are attached. Furthermore, if the default logger has no log level set, the log level will be set to DEBUG. (#3324)

• Add method argument to session.ws_connect(). Sometimes server API requires a different HTTP method for WebSocket connection establishment. For example, Docker exec needs POST. (#3378)

• Create a task per request handling. (#3406)

Bugfixes

• Enable passing access_log_class via handler_args (#3158)

• Return empty bytes with end-of-chunk marker in empty stream reader. (#3186)

• Accept CIMultiDictProxy instances for headers argument in web.Response constructor. (#3207)

• Don’t uppercase HTTP method in parser (#3233)

• Make method match regexp RFC-7230 compliant (#3235)

• Add app.pre_frozen state to properly handle startup signals in sub-applications. (#3237)

• Enhanced parsing and validation of helpers.BasicAuth.decode. (#3239)

• Change imports from collections module in preparation for 3.8. (#3258)

• Ensure Host header is added first to ClientRequest to better replicate browser (#3265)

• Fix forward compatibility with Python 3.8: importing ABCs directly from the collections module will not be supported anymore. (#3273)

• Keep the query string by normalize_path_middleware. (#3278)

• Fix missing parameter raise_for_status for aiohttp.request() (#3290)

• Bracket IPv6 addresses in the HOST header (#3304)

• Fix default message for server ping and pong frames. (#3308)

• Fix tests/test_connector.py typo and tests/autobahn/server.py duplicate loop def. (#3337)

• Fix false-negative indicator end_of_HTTP_chunk in StreamReader.readchunk function (#3361)

• Release HTTP response before raising status exception (#3364)

• Fix task cancellation when sendfile() syscall is used by static file handling. (#3383)

• Fix stack trace for asyncio.TimeoutError which was not logged, when it is caught in the handler. (#3414)

Improved Documentation

• Improve documentation of Application.make_handler parameters. (#3152)

• Fix BaseRequest.raw_headers doc. (#3215)

• Fix typo in TypeError exception reason in web.Application._handle (#3229)

• Make server access log format placeholder %b documentation reflect behavior and docstring. (#3307)

Deprecations and Removals

• Deprecate modification of session.requote_redirect_url (#2278)

• Deprecate stream.unread_data() (#3260)

• Deprecated use of boolean in resp.enable_compression() (#3318)

• Encourage creation of aiohttp public objects inside a coroutine (#3331)

• Drop dead Connection.detach() and Connection.writer. Both methods were broken for more than 2 years. (#3358)

• Deprecate app.loop, request.loop, client.loop and connector.loop properties. (#3374)

• Deprecate explicit debug argument. Use asyncio debug mode instead. (#3381)

• Deprecate body parameter in HTTPException (and derived classes) constructor. (#3385)

• Deprecate bare connector close, use async with connector: and await connector.close() instead. (#3417)

• Deprecate obsolete read_timeout and conn_timeout in ClientSession constructor. (#3438)

Misc

• #3341, #3351