flake8-trio

A highly opinionated flake8 plugin for Trio-related problems.

This can include anything from outright bugs, to pointless/dead code, to likely performance issues, to minor points of idiom that might signal a misunderstanding.

It may well be too noisy for anyone with different opinions, that's OK.

Pairs well with flake8-async and flake8-bugbear.

Installation

pip install flake8-trio

List of warnings

• TRIO100: a with trio.fail_after(...): or with trio.move_on_after(...): context does not contain any await statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
• TRIO101: yield inside a nursery or cancel scope is only safe when implementing a context manager - otherwise, it breaks exception handling.
• TRIO102: it's unsafe to await inside finally: or except BaseException/trio.Cancelled unless you use a shielded cancel scope with a timeout.
• TRIO103: except BaseException and except trio.Cancelled with a code path that doesn't re-raise.
• TRIO104: Cancelled and BaseException must be re-raised - when a user tries to return or raise a different exception.
• TRIO105: Calling a trio async function without immediately awaiting it.
• TRIO106: trio must be imported with import trio for the linter to work.
• TRIO107: exit or return from async function with no guaranteed checkpoint or exception since function definition.
• TRIO108: exit, yield or return from async iterable with no guaranteed checkpoint since possible function entry (yield or function definition) Checkpoints are await, async for, and async with (on one of enter/exit).
• TRIO109: Async function definition with a timeout parameter - use trio.[fail/move_on]_[after/at] instead
• TRIO110: while <condition>: await trio.sleep() should be replaced by a trio.Event.
• TRIO111: Variable, from context manager opened inside nursery, passed to start[_soon] might be invalidly accesed while in use, due to context manager closing before the nursery. This is usually a bug, and nurseries should generally be the inner-most context manager.
• TRIO112: nursery body with only a call to nursery.start[_soon] and not passing itself as a parameter can be replaced with a regular function call.

Changelog

CalVer, YY.month.patch

22.8.7

• TRIO107+108 now ignores asynccontextmanagers, since both __aenter__ and __aexit__ should checkpoint. async with is also treated as checkpointing on both enter and exit.
• TRIO107 now completely ignores any function whose body consists solely of ellipsis, pass, or string constants.
• TRIO103, 107 and 108 now inspects while conditions and for iterables to avoid false alarms on a couple cases where the loop body is guaranteed to run at least once.

22.8.6

• TRIO103 now correctly handles raises in loops, i.e. raise in else is guaranteed to run unless there's a break in the body.

22.8.5

• Add TRIO111: Variable, from context manager opened inside nursery, passed to start[_soon] might be invalidly accesed while in use, due to context manager closing before the nursery. This is usually a bug, and nurseries should generally be the inner-most context manager.
• Add TRIO112: this single-task nursery could be replaced by awaiting the function call directly.

22.8.4

• Fix TRIO108 raising errors on yields in some sync code.
• TRIO109 now skips all decorated functions to avoid false alarms

22.8.3

• TRIO108 now gives multiple error messages; one for each path lacking a guaranteed checkpoint

22.8.2

• Merged TRIO108 into TRIO107
• TRIO108 now handles checkpointing in async iterators

22.8.1

• Added TRIO109: Async definitions should not have a timeout parameter. Use trio.[fail/move_on]_[at/after]
• Added TRIO110: while <condition>: await trio.sleep() should be replaced by a trio.Event.

22.7.6

• Extend TRIO102 to also check inside except BaseException and except trio.Cancelled
• Extend TRIO104 to also check for yield
• Update error messages on TRIO102 and TRIO103

22.7.5

• Add TRIO103: except BaseException or except trio.Cancelled with a code path that doesn't re-raise
• Add TRIO104: "Cancelled and BaseException must be re-raised" if user tries to return or raise a different exception.
• Added TRIO107: Async functions must have at least one checkpoint on every code path, unless an exception is raised
• Added TRIO108: Early return from async function must have at least one checkpoint on every code path before it.

22.7.4

• Added TRIO105 check for not immediately awaiting async trio functions.
• Added TRIO106 check that trio is imported in a form that the plugin can easily parse.

22.7.3

• Added TRIO102 check for unsafe checkpoints inside finally: blocks

22.7.2

• Avoid TRIO100 false-alarms on cancel scopes containing async for or async with.

22.7.1

• Initial release with TRIO100 and TRIO101