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A lightweight Python asyncio HTTP client
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A lightweight Python asyncio HTTP/1.1 client. No additional tasks are created; all code is in a single module; and other than the standard library only a single dependency is required, aiodnsresolver.

Connections are DNS-aware, in that they are only re-used if they match a current A record for the domain.


pip install lowhaio


The API is streaming-first: for both request and response bodies, asynchronous iterators are used.

import os
from lowhaio import Pool

request, _ = Pool()

path = 'my.file'
content_length = str(os.stat(path).st_size).encode()
async def file_data():
    with open(path, 'rb') as file:
        for chunk in iter(lambda:, b''):
            yield chunk

code, headers, body = await request(
    b'POST', '',
    params=(), headers=((b'content-length': content_length),), body=file_data,
async for chunk in body:

However, there are helper functions streamed and buffered when this isn't required or possible.

from lowhaio import Pool, streamed, buffered

request, _ = Pool()

content = b'some-data'
content_length = b'9'
code, headers, body = await request(
    b'POST', '',
    params=(), headers=((b'content-length': content_length),), body=streamed(content),

response = await buffered(body)


The only header automatically added to requests is the host header, which is the idna/punycode-encoded domain name from the requested URL.


Exceptions raised are subclasses of HttpError. If a lower-level exception caused this, it is set in the __cause__ attribute of the HttpError

Exceptions before any data is sent are instances of HttpConnectionError, and after data is sent, HttpDataError. This is to make it possible to know if non-idempotent requests can be retried.


The scope of the core functions is restricted to:

  • (TLS) connection opening, closing and pooling;
  • passing and receiving HTTP headers and streaming bodies;
  • decoding chunked responses;
  • raising exceptions on timeouts.

This is to make the core behaviour useful to a reasonable range of uses, but to not include what can be added by layer(s) on top. Specifically not included:

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