Release history

Trio 0.3.0 (2017-12-28)


  • Simplified nurseries: In Trio, the rule used to be that “parenting is a full time job”, meaning that after a task opened a nursery and spawned some children into it, it had to immediately block in __aexit__ to supervise the new children, or else exception propagation wouldn’t work. Also there was some elaborate machinery to let you replace this supervision logic with your own custom supervision logic. Thanks to new advances in task-rearing technology, parenting is no longer a full time job! Now the supervision happens automatically in the background, and essentially the body of a async with trio.open_nursery() block acts just like a task running inside the nursery. This is important: it makes it possible for libraries to abstract over nursery creation. For example, if you have a Websocket library that needs to run a background task to handle Websocket pings, you can now do that with async with open_websocket(...) as ws: ..., and that can run a task in the background without your users having to worry about parenting it. And don’t worry, you can still make custom supervisors; it turned out all that spiffy machinery was actually redundant and didn’t provide much value. (#136)
  • Trio socket methods like bind and connect no longer require “pre-resolved” numeric addresses; you can now pass regular hostnames and Trio will implicitly resolve them for you. (#377)


  • Fixed some corner cases in Trio socket method implicit name resolution to better match stdlib behavior. Example: sock.bind(("", port)) now binds to the wildcard address instead of raising an error. (#277)

Deprecations and Removals

  • Removed everything that was deprecated in 0.2.0; see the 0.2.0 release notes below for details.
  • As was foretold in the v0.2.0 release notes, the bind method on Trio sockets is now async. Please update your calls or – better yet – switch to our shiny new high-level networking API, like serve_tcp(). (#241)
  • The resolve_local_address and resolve_remote_address methods on Trio sockets have been deprecated; these are unnecessary now that you can just pass your hostnames directly to the socket methods you want to use. (#377)

Trio 0.2.0 (2017-12-06)

Trio 0.2.0 contains changes from 14 contributors, and brings major new features and bug fixes, as well as a number of deprecations and a very small number of backwards incompatible changes. We anticipate that these should be easy to adapt to, but make sure to read about them below, and if you’re using Trio then remember to read and subscribe to issue #1.


Breaking changes and deprecations

Trio is a young and ambitious project, but it also aims to become a stable, production-quality foundation for async I/O in Python. Therefore, our approach for now is to provide deprecation warnings where-ever possible, but on a fairly aggressive cycle as we push towards stability. If you use Trio you should read and subscribe to issue #1. We’d also welcome feedback on how this approach is working, whether our deprecation warnings could be more helpful, or anything else.

The tl;dr is: stop using socket.bind if you can, and then fix everything your test suite warns you about.

Upcoming breaking changes without warnings (i.e., stuff that works in 0.2.0, but won’t work in 0.3.0):

  • In the next release, the bind method on Trio socket objects will become async (#241). Unfortunately, there’s no good way to provide a warning here. We recommend switching to the new highlevel networking APIs like serve_tcp(), which will insulate you from this change.

Breaking changes (i.e., stuff that could theoretically break a program that worked on 0.1.0):

  • trio.socket no longer attempts to normalize or modernize socket options across different platforms. The high-level networking API now handles that, freeing trio.socket to focus on giving you raw, unadulterated BSD sockets.
  • When a socket sendall call was cancelled, it used to attach some metadata to the exception reporting how much data was actually sent. It no longer does this, because in common configurations like an SSLStream wrapped around a SocketStream it becomes ambiguous which “level” the partial metadata applies to, leading to confusion and bugs. There is no longer any way to tell how much data was sent after a sendall is cancelled.
  • The trio.socket.getprotobyname() function is now async, like it should have been all along. I doubt anyone will ever use it, but that’s no reason not to get the details right.
  • The trio.socket functions getservbyport, getservbyname, and getfqdn have been removed, because they were obscure, buggy, and obsolete. Use getaddrinfo() instead.

Upcoming breaking changes with warnings (i.e., stuff that in 0.2.0 will work but will print loud complaints, and that won’t work in 0.3.0):

Unfortunately, a limitation in PyPy3 5.8 breaks our deprecation handling for some renames. (Attempting to use the old names will give an unhelpful error instead of a helpful warning.) This does not affect CPython, or PyPy3 5.9+.

Other changes

  • run_sync_in_worker_thread() now has a robust mechanism for applying capacity limits to the number of concurrent threads (#10, #57, #156)

  • New support for tests to cleanly hook hostname lookup and socket operations: see Virtual networking for testing. In addition, trio.socket.SocketType is now an empty abstract base class, with the actual socket class made private. This shouldn’t effect anyone, since the only thing you could directly use it for in the first place was isinstance checks, and those still work (#170)

  • New class StrictFIFOLock

  • New exception ResourceBusyError

  • The trio.hazmat.ParkingLot class (which is used to implement many of Trio’s synchronization primitives) was rewritten to be simpler and faster (#272, #287)

  • It’s generally true that if you’re using Trio you have to use Trio functions, if you’re using asyncio you have to use asyncio functions, and so forth. (See the discussion of the “async sandwich” in the Trio tutorial for more details.) So for example, this isn’t going to work:

    async def main():
        # asyncio here
        await asyncio.sleep(1)
    # trio here

    Trio now reliably detects if you accidentally do something like this, and gives a helpful error message.

  • Trio now also has special error messages for several other common errors, like doing (should be

  • trio.socket now handles non-ascii domain names using the modern IDNA 2008 standard instead of the obsolete IDNA 2003 standard (#11)

  • When an Instrument raises an unexpected error, we now route it through the logging module instead of printing it directly to stderr. Normally this produces exactly the same effect, but this way it’s more configurable. (#306)

  • Fixed a minor race condition in IOCP thread shutdown on Windows (#81)

  • Control-C handling on Windows now uses signal.set_wakeup_fd() and should be more reliable (#42)

  • takes a new keyword argument restrict_keyboard_interrupt_to_checkpoints

  • New attributes allow more detailed introspection of the task tree: nursery.child_tasks, Task.child_nurseries, nursery.parent_task, Task.parent_nursery

  • trio.testing.wait_all_tasks_blocked() now takes a tiebreaker= argument. The main use is to allow MockClock’s auto-jump functionality to avoid interfering with direct use of wait_all_tasks_blocked() in the same test.

  • MultiError.catch() now correctly preserves __context__, despite Python’s best attempts to stop us (#165)

  • It is now possible to take weakrefs to Lock and many other classes (#331)

  • Fix sock.accept() for IPv6 sockets (#164)

  • PyCharm (and hopefully other IDEs) can now offer better completions for the trio and trio.hazmat modules (#314)

  • Trio now uses yapf to standardize formatting across the source tree, so we never have to think about whitespace again.

  • Many documentation improvements

Trio 0.1.0 (2017-03-10)

  • Initial release.