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Use standalone result library instead #494

Fuyukai opened this Issue Apr 14, 2018 · 5 comments


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Fuyukai commented Apr 14, 2018

As said in #477, the Result objects got split out into a separate library ( There's no point duplicating all the code in Trio - better to depend on it directly.


  • Gut result code inside of Trio
  • Use the results from outcome instead.

Maybe make the current objects in Trio simply redirect to the outcome objects until the next version, deprecating them in 0.5 (with a redirect) and removing in 0.6.


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njsmith commented Apr 14, 2018

CC @RazerM

There may be a small bit of awkwardness here because outcome also tweaked the API: Result.capture got replaced with outcome.capture instead of outcome.Outcome.capture. This is probably a good change on its own merits (the only reason I stuck capture onto the Result type was because I didn't have a proper module to put it on), but it means we can't just alias Result to outcome.Outcome and have everything work. The simplest thing might be to do:

class Result(Outcome):
    def capture(...):

    async def acapture(...):

Result.register(Outcome)  # yes, they're subclasses of each other, what's wrong with that?

Gross hacks are fine because it's just a temporary shim that we'll throw away in a few versions after the deprecation period...


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RazerM commented Apr 14, 2018


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njsmith commented Apr 15, 2018

Bah, fine. I bet CPython isn't any fun at parties either.

In this case I think it would be enough to register just the concrete classes outcome.Value and outcome.Error.


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Fuyukai commented Apr 15, 2018

The issue with this is that I cannot see a way to meet all of the following:

  • Keep the same API (i.e. capture/acapture) for all types
  • Make isinstance() work properly with both outcome and _core._result types

If the first point is lifted, it can simply be Value = outcome.Value / Error = outcome.Error and register them as virtual subclasses of Result.


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njsmith commented Apr 15, 2018

Oh, you mean because right now someone could write Value.capture(...), and that would break if we do Value = outcome.Value? I guess that's technically true, but I doubt anyone's ever done that and I'm fine with just ignoring it. So I think I'm agreeing with your suggestion.

njsmith added a commit to Fuyukai/trio that referenced this issue Apr 21, 2018

Fix __deprecated_attributes__ usage
- The dict needs to live in the module where the deprecated attributes
  are; so here it needs to be hazmat.__deprecated_attributes__.
  (Maybe it would be less confusing to put this in, I don't

- Don't export the symbols from trio.hazmat using normal mechanisms;
  that overrides the __deprecated_attributes__ mechanism.

- Then since they're no longer in hazmat, we can't say that
  trio.hazmat.Value resolves to the value trio.hazmat.Value, so point
  the __deprecated_attributes__ entries directly at trio._core._result.*

- In fact, let's stop exporting them from trio._core entirely.

- And then this reveals two tests that were still referring to
  trio._core.Error, so fix those.

Confirmed manually that with these changes I get correct values and
warnings for accessing the public attributes:

In [2]: trio.hazmat.Result
/home/njs/.user-python3.5-64bit/bin/ipython:1: TrioDeprecationWarning: trio.hazmat.Result is deprecated since Trio 0.5.0; use outcome.Outcome instead (python-trio#494)
Out[2]: trio._core._result.Result  # class

In [3]: trio.hazmat.Value
/home/njs/.user-python3.5-64bit/bin/ipython:1: TrioDeprecationWarning: trio.hazmat.Value is deprecated since Trio 0.5.0; use outcome.Value instead (python-trio#494)
Out[3]: outcome.Value  # class

In [4]: trio.hazmat.Error
/home/njs/.user-python3.5-64bit/bin/ipython:1: TrioDeprecationWarning: trio.hazmat.Error is deprecated since Trio 0.5.0; use outcome.Error instead (python-trio#494)
Out[4]: outcome.Error  # class

@Fuyukai Fuyukai closed this in #503 Apr 21, 2018

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