docs/client_quickstart.rst
.. currentmodule:: aiohttp
.. _aiohttp-client-quickstart:
Eager to get started? This page gives a good introduction in how to get started with aiohttp client API.
First, make sure that aiohttp is :ref:installed <aiohttp-installation> and up-to-date
Let's get started with some simple examples.
Begin by importing the aiohttp module, and asyncio::
import aiohttp
import asyncio
Now, let's try to get a web-page. For example let's query
http://httpbin.org/get::
async def main():
async with aiohttp.ClientSession() as session:
async with session.get('http://httpbin.org/get') as resp:
print(resp.status)
print(await resp.text())
asyncio.run(main())
Now, we have a :class:ClientSession called session and a
:class:ClientResponse object called resp. We can get all the
information we need from the response. The mandatory parameter of
:meth:ClientSession.get coroutine is an HTTP url (:class:str or
class:yarl.URL instance).
In order to make an HTTP POST request use :meth:ClientSession.post coroutine::
session.post('http://httpbin.org/post', data=b'data')
Other HTTP methods are available as well::
session.put('http://httpbin.org/put', data=b'data')
session.delete('http://httpbin.org/delete')
session.head('http://httpbin.org/get')
session.options('http://httpbin.org/get')
session.patch('http://httpbin.org/patch', data=b'data')
To make several requests to the same site more simple, the parameter base_url
of :class:ClientSession constructor can be used. For example to request different
endpoints of http://httpbin.org can be used the following code::
async with aiohttp.ClientSession('http://httpbin.org') as session:
async with session.get('/get'):
pass
async with session.post('/post', data=b'data'):
pass
async with session.put('/put', data=b'data'):
pass
.. note::
Don't create a session per request. Most likely you need a session per application which performs all requests together.
More complex cases may require a session per site, e.g. one for Github and other one for Facebook APIs. Anyway making a session for every request is a very bad idea.
A session contains a connection pool inside. Connection reusage and keep-alive (both are on by default) may speed up total performance.
You may find more information about creating persistent sessions
in :ref:aiohttp-persistent-session.
A session context manager usage is not mandatory
but await session.close() method
should be called in this case, e.g.::
session = aiohttp.ClientSession()
async with session.get('...'):
# ...
await session.close()
You often want to send some sort of data in the URL's query string. If
you were constructing the URL by hand, this data would be given as key/value
pairs in the URL after a question mark, e.g. httpbin.org/get?key=val.
aiohttp allows you to provide these arguments as a :class:dict, using the
params keyword argument. As an example, if you wanted to pass
key1=value1 and key2=value2 to httpbin.org/get, you would use the
following code::
params = {'key1': 'value1', 'key2': 'value2'}
async with session.get('http://httpbin.org/get',
params=params) as resp:
expect = 'http://httpbin.org/get?key1=value1&key2=value2'
assert str(resp.url) == expect
You can see that the URL has been correctly encoded by printing the URL.
For sending data with multiple values for the same key
:class:~multidict.MultiDict may be used; the library support nested lists
({'key': ['value1', 'value2']}) alternative as well.
It is also possible to pass a list of 2 item tuples as parameters, in that case you can specify multiple values for each key::
params = [('key', 'value1'), ('key', 'value2')]
async with session.get('http://httpbin.org/get',
params=params) as r:
expect = 'http://httpbin.org/get?key=value2&key=value1'
assert str(r.url) == expect
You can also pass :class:str content as param, but beware -- content
is not encoded by library. Note that + is not encoded::
async with session.get('http://httpbin.org/get',
params='key=value+1') as r:
assert str(r.url) == 'http://httpbin.org/get?key=value+1'
.. note::
aiohttp internally performs URL canonicalization before sending request.
Canonicalization encodes host part by :term:IDNA codec and applies
:term:requoting to path and query parts.
For example URL('http://example.com/путь/%30?a=%31') is converted to
URL('http://example.com/%D0%BF%D1%83%D1%82%D1%8C/0?a=1').
Sometimes canonicalization is not desirable if server accepts exact representation and does not requote URL itself.
To disable canonicalization use encoded=True parameter for URL construction::
await session.get(
URL('http://example.com/%30', encoded=True))
.. warning::
Passing params overrides encoded=True, never use both options.
We can read the content of the server's response and its status code. Consider the GitHub time-line again::
async with session.get('https://api.github.com/events') as resp:
print(resp.status)
print(await resp.text())
prints out something like::
200
'[{"created_at":"2015-06-12T14:06:22Z","public":true,"actor":{...
aiohttp automatically decodes the content from the server. You can
specify custom encoding for the :meth:~ClientResponse.text method::
await resp.text(encoding='windows-1251')
You can also access the response body as bytes, for non-text requests::
print(await resp.read())
::
b'[{"created_at":"2015-06-12T14:06:22Z","public":true,"actor":{...
The gzip and deflate transfer-encodings are automatically
decoded for you.
You can enable brotli transfer-encodings support,
just install Brotli <https://pypi.org/project/Brotli/>_
or brotlicffi <https://pypi.org/project/brotlicffi/>_.
You can enable zstd transfer-encodings support,
install backports.zstd <https://pypi.org/project/backports.zstd/>_.
If you are using Python >= 3.14, no dependency should be required.
Any of session's request methods like :func:request,
:meth:ClientSession.get, :meth:ClientSession.post etc. accept
json parameter::
async with aiohttp.ClientSession() as session: await session.post(url, json={'test': 'object'})
By default session uses python's standard :mod:json module for
serialization. But it is possible to use a different
serializer. :class:ClientSession accepts json_serialize and
json_serialize_bytes parameters::
import orjson
async with aiohttp.ClientSession( json_serialize_bytes=orjson.dumps) as session: await session.post(url, json={'test': 'object'})
.. note::
orjson library is faster than standard :mod:json and is actively
maintained. Since orjson.dumps returns :class:bytes, pass it via
the json_serialize_bytes parameter to avoid unnecessary
encoding/decoding overhead.
There's also a built-in JSON decoder, in case you're dealing with JSON data::
async with session.get('https://api.github.com/events') as resp:
print(await resp.json())
In case that JSON decoding fails, :meth:~ClientResponse.json will
raise an exception. It is possible to specify custom encoding and
decoder functions for the :meth:~ClientResponse.json call.
.. note::
The methods above reads the whole response body into memory. If you are
planning on reading lots of data, consider using the streaming response
method documented below.
While methods :meth:~ClientResponse.read,
:meth:~ClientResponse.json and :meth:~ClientResponse.text are very
convenient you should use them carefully. All these methods load the
whole response in memory. For example if you want to download several
gigabyte sized files, these methods will load all the data in
memory. Instead you can use the :attr:~ClientResponse.content
attribute. It is an instance of the :class:aiohttp.StreamReader
class. The gzip and deflate transfer-encodings are
automatically decoded for you::
async with session.get('https://api.github.com/events') as resp:
await resp.content.read(10)
In general, however, you should use a pattern like this to save what is being streamed to a file::
with open(filename, 'wb') as fd:
async for chunk in resp.content.iter_chunked(chunk_size):
fd.write(chunk)
It is not possible to use :meth:~ClientResponse.read,
:meth:~ClientResponse.json and :meth:~ClientResponse.text after
explicit reading from :attr:~ClientResponse.content.
Typically, you want to send some form-encoded data -- much like an HTML form. To do this, simply pass a dictionary to the data argument. Your dictionary of data will automatically be form-encoded when the request is made::
payload = {'key1': 'value1', 'key2': 'value2'}
async with session.post('http://httpbin.org/post',
data=payload) as resp:
print(await resp.text())
::
{
...
"form": {
"key2": "value2",
"key1": "value1"
},
...
}
If you want to send data that is not form-encoded you can do it by
passing a :class:bytes instead of a :class:dict. This data will be
posted directly and content-type set to 'application/octet-stream' by
default::
async with session.post(url, data=b'\x00Binary-data\x00') as resp:
...
If you want to send JSON data::
async with session.post(url, json={'example': 'test'}) as resp:
...
To send text with appropriate content-type just use data argument::
async with session.post(url, data='Тест') as resp:
...
To upload Multipart-encoded files::
url = 'http://httpbin.org/post'
files = {'file': open('report.xls', 'rb')}
await session.post(url, data=files)
You can set the filename and content_type explicitly::
url = 'http://httpbin.org/post'
data = aiohttp.FormData()
data.add_field('file',
open('report.xls', 'rb'),
filename='report.xls',
content_type='application/vnd.ms-excel')
await session.post(url, data=data)
If you pass a file object as data parameter, aiohttp will stream it to
the server automatically. Check :class:~aiohttp.StreamReader
for supported format information.
.. seealso:: :ref:aiohttp-multipart
:mod:aiohttp supports multiple types of streaming uploads, which allows you to
send large files without reading them into memory.
As a simple case, simply provide a file-like object for your body::
with open("massive-body", "rb") as f:
await session.post("https://httpbin.org/post", data=f)
Or you can provide an asynchronous generator, for example to generate data on the fly::
async def data_generator(): for i in range(10): yield f"line {i}\n".encode()
async with session.post("https://httpbin.org/post", data=data_generator()) as resp: print(await resp.text())
.. warning::
Async generators and other non-rewindable data sources
(such as :class:~aiohttp.StreamReader) cannot be replayed if a
redirect occurs (for example, HTTP 307 or 308). If the request body
has already been streamed, :mod:aiohttp raises
:class:~aiohttp.ClientPayloadError.
If your endpoint may redirect, either:
bytes.allow_redirects=False and handle them manually.Because the :attr:~aiohttp.ClientResponse.content attribute is a
:class:~aiohttp.StreamReader (provides async iterator protocol), you
can chain get and post requests together::
resp = await session.get('http://python.org') await session.post('http://httpbin.org/post', data=resp.content)
.. _aiohttp-client-websockets:
:mod:aiohttp works with client websockets out-of-the-box.
You have to use the :meth:aiohttp.ClientSession.ws_connect coroutine
for client websocket connection. It accepts a url as a first
parameter and returns :class:ClientWebSocketResponse, with that
object you can communicate with websocket server using response's
methods::
async with session.ws_connect('http://example.org/ws') as ws: async for msg in ws: if msg.type == aiohttp.WSMsgType.TEXT: if msg.data == 'close cmd': await ws.close() break else: await ws.send_str(msg.data + '/answer') elif msg.type == aiohttp.WSMsgType.ERROR: break
You must use the only websocket task for both reading (e.g. await ws.receive() or async for msg in ws:) and writing but may have
multiple writer tasks which can only send data asynchronously (by
await ws.send_str('data') for example).
.. _aiohttp-client-timeouts:
Timeout settings are stored in :class:ClientTimeout data structure.
By default aiohttp uses a total 300 seconds (5min) timeout, it means that the
whole operation should finish in 5 minutes. In order to allow time for DNS fallback,
the default sock_connect timeout is 30 seconds.
The value could be overridden by timeout parameter for the session (specified in seconds)::
timeout = aiohttp.ClientTimeout(total=60)
async with aiohttp.ClientSession(timeout=timeout) as session:
...
Timeout could be overridden for a request like :meth:ClientSession.get::
async with session.get(url, timeout=timeout) as resp:
...
Supported :class:ClientTimeout fields are:
total
The maximal number of seconds for the whole operation including connection
establishment, request sending and response reading.
connect
The maximal number of seconds for
connection establishment of a new connection or
for waiting for a free connection from a pool if pool connection
limits are exceeded.
sock_connect
The maximal number of seconds for connecting to a peer for a new connection, not
given from a pool.
sock_read
The maximal number of seconds allowed for period between reading a new
data portion from a peer.
``ceil_threshold``
The threshold value to trigger ceiling of absolute timeout values.
All fields are floats, None or 0 disables a particular timeout check, see the
:class:ClientTimeout reference for defaults and additional details.
Thus the default timeout is::
aiohttp.ClientTimeout(total=5*60, connect=None, sock_connect=None, sock_read=None, ceil_threshold=5)
.. note::
aiohttp ceils timeout if the value is equal or greater than 5
seconds. The timeout expires at the next integer second greater than
current_time + timeout.
The ceiling is done for the sake of optimization, when many concurrent tasks are scheduled to wake-up at the almost same but different absolute times. It leads to very many event loop wakeups, which kills performance.
The optimization shifts absolute wakeup times by scheduling them to exactly the same time as other neighbors, the loop wakes up once-per-second for timeout expiration.
Smaller timeouts are not rounded to help testing; in the real life network
timeouts usually greater than tens of seconds. However, the default threshold
value of 5 seconds can be configured using the ceil_threshold parameter.