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Trio – a friendly Python library for async concurrency and I/O

.. Github carefully breaks rendering of SVG directly out of the repo,
so we have to redirect through cdn.rawgit.com
See:
https://github.com/isaacs/github/issues/316
https://github.com/github/markup/issues/556#issuecomment-288581799
I also tried rendering to PNG and linking to that locally, which
"works" in that it displays the image, but for some reason it
ignores the width and align directives, so it's actually pretty
useless...

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The Trio project's goal is to produce a production-quality,
permissively licensed <https://github.com/python-trio/trio/blob/master/LICENSE>__,
async/await-native I/O library for Python. Like all async libraries,
its main purpose is to help you write programs that do multiple
things at the same time with parallelized I/O. A web spider that
wants to fetch lots of pages in parallel, a web server that needs to
juggle lots of downloads and websocket connections at the same time, a
process supervisor monitoring multiple subprocesses... that sort of
thing. Compared to other libraries, Trio attempts to distinguish
itself with an obsessive focus on usability and
correctness. Concurrency is complicated; we try to make it easy
to get things right.

Trio was built from the ground up to take advantage of the latest Python features <https://www.python.org/dev/peps/pep-0492/>, and
draws inspiration from many sources <https://github.com/python-trio/trio/wiki/Reading-list>, in
particular Dave Beazley's Curio <https://curio.readthedocs.io/>.
The resulting design is radically simpler than older competitors like
asyncio <https://docs.python.org/3/library/asyncio.html> and
Twisted <https://twistedmatrix.com/>, yet just as capable. Trio is
the Python I/O library I always wanted; I find it makes building
I/O-oriented programs easier, less error-prone, and just plain more
fun. Perhaps you'll find the same <https://github.com/python-trio/trio/wiki/Testimonials>.

This project is young and still somewhat experimental: the overall
design is solid and the existing features are fully tested and
documented, but you may encounter missing functionality or rough
edges. We do encourage you to use it, but you should read and subscribe to issue #1 <https://github.com/python-trio/trio/issues/1>__ to get warning and a
chance to give feedback about any compatibility-breaking changes.

Where to next?

I want to try it out! Awesome! We have a friendly tutorial <https://trio.readthedocs.io/en/stable/tutorial.html>__ to get you
started; no prior experience with async coding is required.

Ugh, I don't want to read all that – show me some code! If you're
impatient, then here's a simple concurrency example <https://trio.readthedocs.io/en/stable/tutorial.html#tutorial-example-tasks-intro>,
an echo client <https://trio.readthedocs.io/en/stable/tutorial.html#tutorial-echo-client-example>,
and an echo server <https://trio.readthedocs.io/en/stable/tutorial.html#tutorial-echo-server-example>__.

How does Trio make programs easier to read and reason about than
competing approaches? Trio is based on a new way of thinking that we
call "structured concurrency". The best theoretical introduction is
the article Notes on structured concurrency, or: Go statement considered harmful <https://vorpus.org/blog/notes-on-structured-concurrency-or-go-statement-considered-harmful/>.
Or, check out this talk at PyCon 2018 <https://www.youtube.com/watch?v=oLkfnc_UMcE> to see a
demonstration of implementing the "Happy Eyeballs" algorithm in an
older library versus Trio.

Cool, but will it work on my system? Probably! As long as you have
some kind of Python 3.5-or-better (CPython or the latest PyPy3 are
both fine), and are using Linux, macOS, or Windows, then Trio should
absolutely work. *BSD and illumos likely work too, but we don't have
testing infrastructure for them. And all of our dependencies are pure
Python, except for CFFI on Windows, and that has wheels available, so
installation should be easy.

I tried it but it's not working. Sorry to hear that! You can try
asking for help in our chat room <https://gitter.im/python-trio/general>__ or forum <https://trio.discourse.group>, filing a bug <https://github.com/python-trio/trio/issues/new>, or posting a question on StackOverflow <https://stackoverflow.com/questions/ask?tags=python+python-trio>__,
and we'll do our best to help you out.

Trio is awesome and I want to help make it more awesome! You're
the best! There's tons of work to do – filling in missing
functionality, building up an ecosystem of Trio-using libraries,
usability testing (e.g., maybe try teaching yourself or a friend to
use Trio and make a list of every error message you hit and place
where you got confused?), improving the docs, ... check out our guide for contributors <https://trio.readthedocs.io/en/stable/contributing.html>__!

I don't have any immediate plans to use it, but I love geeking out
about I/O library design! That's a little weird? But let's be
honest, you'll fit in great around here. We have a whole sub-forum for discussing structured concurrency <https://trio.discourse.group/c/structured-concurrency>__ (developers
of other systems welcome!). Or check out our discussion of design choices <https://trio.readthedocs.io/en/stable/design.html#user-level-api-principles>,
reading list <https://github.com/python-trio/trio/wiki/Reading-list>, and
issues tagged design-discussion <https://github.com/python-trio/trio/labels/design%20discussion>__.

I want to make sure my company's lawyers won't get angry at me! No
worries, Trio is permissively licensed under your choice of MIT or
Apache 2. See LICENSE <https://github.com/python-trio/trio/blob/master/LICENSE>__ for details.

Code of conduct

Contributors are requested to follow our code of conduct <https://trio.readthedocs.io/en/stable/code-of-conduct.html>__ in all
project spaces.