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Small utility library for generic coroutine-driven, asynchronous-oriented programming in Python +3.4.

Built on top of asyncio, paco provides missing capabilities from Python stdlib to write asynchronous cooperative multitasking in a nice-ish way + some convenient functional helpers.

Note: paco is still beta.


  • Simple and idiomatic API, extending Python stdlib with async coroutines gotchas.
  • Built-in configurable control-flow concurrency support.
  • Useful iterables, decorators and functors.
  • Provides coroutine-ready compose, throttle, partial, until, race and other functional helpers.
  • Asynchronous coroutine port of Python built-in functions: filter, map, dropwhile, filterfalse, reduce...
  • Coroutines control flow and higher-order functions goodness.
  • Better asyncio.gather() and asyncio.wait() implementations with optional concurrency control and ordered results.
  • Good interoperability with asyncio and Python stdlib functions.
  • Partially ports Python stdlib higher-order functions and iterables to be used in async coroutines world.
  • Works with both async/await and yield from coroutines syntax.
  • Small and dependency free.
  • Compatible with Python +3.4.


Using pip package manager:

pip install paco

Or install the latest sources from Github:

pip install -e git+git://



Asynchronously execute multiple HTTP requests concurrently.

import paco
import aiohttp
import asyncio

async def fetch(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as resp:
            return resp

async def fetch_urls():
    urls = [

    # Map concurrent executor with concurrent limit of 3
    responses = await, urls, limit=3)

    for res in responses:
        print('Status:', res.status)

loop = asyncio.get_event_loop()


MIT - Tomas Aparicio

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