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Small utility library for coroutine-based asynchronous generic programming

Project description

paco Build Status PyPI Coverage Status Documentation Status Stability Quality Versions

Small and idiomatic utility library for coroutine-driven asynchronous generic programming in Python +3.4.

Built on top of asyncio, paco provides missing capabilities from Python stdlib in order to write asynchronous cooperative multitasking in a nice-ish way. Also, paco aims to port some of functools and itertools standard functions to the asynchronous world.

paco can be your utility belt to deal with asynchronous, I/O-bound, non-blocking concurrent code in a cleaner and idiomatic way.


  • Simple and idiomatic API, extending Python stdlib with async coroutines gotchas.

  • Built-in configurable control-flow concurrency support (throttle).

  • No fancy abstractions: it just works with the plain asynchronous coroutines.

  • Useful iterables, decorators, functors and convenient helpers.

  • Coroutine-based functional helpers: compose, throttle, partial, timeout, times, until, race

  • Asynchronous coroutines port of Python built-in functions: filter, map, dropwhile, filterfalse, reduce

  • Supports asynchronous iterables and generators (PEP0525)

  • Concurrent iterables and higher-order functions.

  • Better asyncio.gather() and asyncio.wait() with optional concurrency control and ordered results.

  • Works with both async/await and yield from coroutines syntax.

  • Reliable coroutine timeout limit handler via context manager.

  • Designed for intensive I/O bound concurrent non-blocking tasks.

  • Good interoperability with asyncio and Python stdlib functions.

  • Composable pipelines of functors via | operator overloading.

  • Small and dependency free.

  • Compatible with Python +3.4.


Using pip package manager:

pip install --upgrade paco

Or install the latest sources from Github:

pip install -e git+git://



Asynchronously and concurrently execute multiple HTTP requests.

import paco
import aiohttp

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

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)

# Run in event loop

Concurrent pipeline-style composition of transform functors over an iterable object.

import paco

async def filterer(x):
    return x < 8

async def mapper(x):
    return x * 2

async def drop(x):
    return x < 10

async def reducer(acc, x):
    return acc + x

async def task(numbers):
    return await (numbers
                   | paco.filter(filterer)
                   | paco.dropwhile(drop)
                   | paco.reduce(reducer, initializer=0))

# Run in event loop
number =, 2, 3, 4, 5, 6, 7, 8, 9, 10)))
print('Number:', number) # => 36


MIT - Tomas Aparicio


v0.2.3 / 2018-10-23

  • Merge pull request #42 from dylanjw/fix_syntax_error

  • Use getattr to avoid async keyword

0.2.2 / 2018-10-09

  • Merge pull request #40 from thatmattbone/master

  • add loop param to paco.interval()

  • fix(setup): use space based indentation

  • fix(travis): use cpython 3.7-dev release

  • refactor(errors): use “paco” prefix in exception messages

  • chore(History): add version changes

v0.2.1 / 2018-03-21

  • fix(#37): allow overload function signatures with variadic arguments

  • refactor(timeout_test): remove print statement

  • fix(docs): bad link to API reference

  • refactor(docs): remove codesponsor

v0.2.0 / 2017-10-21

  • refactor(api): API breaking change that modifies behavior by raising any legit exception generated by a coroutine.

  • feat(examples): add examples file

  • feat(v2): v2 pre-release, propagate raise exception if return_exceptions is False

  • refactor(tests): add map error exception assertion test

  • Merge branch ‘master’ of

  • refactor(tests): add map error exception assertion test

  • feat(docs): add sponsor banner

  • feat(docs): add sponsor banner

  • feat(LICENSE): update copyright year

  • Update

v0.1.11 / 2017-01-28

  • feat(api): add paco.interval function.

v0.1.10 / 2017-01-11

  • fix(, fixed return_exceptions kwarg

  • fix( add author email

  • fix(Makefile): remove package file

v0.1.9 / 2017-01-06

  • feat(api): add identity function

  • feat(#31): add thunk function

  • feat(package): add wheel package distribution

  • refactor(wraps): simplify implementation

  • fix(History): remove indentation

v0.1.8 / 2016-12-29

  • feat(requirements): force upgrade setuptools

  • feat(#29): support async iterable and generators

  • fix(docs): link to examples

  • chore(travis): use Python 3.6 stable release

0.1.7 / 2016-12-18

  • feat(#26): add curry function.

0.1.6 / 2016-12-11

  • feat(pipe): isolate pipe operator overload code

  • refactor: decorator and util functions

  • feat(#11): timeout limit context manager.

  • refactor(core): several minor refactors

  • fix(docs): comment out latex sphinx settings

  • fix(docs): use current package version

  • Documentation examples improvements (#27)

  • feat(history): update

  • feat: add pool length magic method

0.1.5 (2016-12-04)

  • fix(#25): allow empty iterables in iterators functions, such as map, filter, reduce.

0.1.4 (2016-11-28)

  • fix(#24): explicitly pass loop instance to asyncio.wait.

0.1.3 (2016-10-27)

  • feat(#17): add flat_map function.

  • feat(#18): add pipeline-style operator overloading composition.

0.1.2 (2016-10-25)

  • fix( fix pip installation.

  • refactor(api): minor refactors in several functions and tests.

0.1.1 (2016-10-24)

  • refactor(name): use new project name.

0.1.0 (2016-10-23)

  • First version (beta)

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