Re: [Django] #34998: Raising a StopIteration in asynchronous mode hangs the request

[Django]

#34998: Raising a StopIteration in asynchronous mode hangs the request
-+-
 Reporter:  Clément Escolano |Owner:  nobody
 Type:   |   Status:  closed
  Cleanup/optimization   |
Component:  Core (Other) |  Version:  4.2
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:   | Triage Stage:
 |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak):

 * status:  new => closed
 * resolution:   => wontfix
 * component:  Uncategorized => Core (Other)
 * type:  Uncategorized => Cleanup/optimization


Comment:

 Thanks for comments!

 Closing as "wontfix" unless someone can prove it's actionable in Django
 itself.

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Re: [Django] #34998: Raising a StopIteration in asynchronous mode hangs the request

[Django]

#34998: Raising a StopIteration in asynchronous mode hangs the request
--+--
 Reporter:  Clément Escolano  |Owner:  nobody
 Type:  Uncategorized |   Status:  new
Component:  Uncategorized |  Version:  4.2
 Severity:  Normal|   Resolution:
 Keywords:| Triage Stage:  Unreviewed
Has patch:  0 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+--

Comment (by Andrew Godwin):

 Hmm yes, this is one of those nasty bugs that reveals the true nature of
 how Python async works.

 In testing this locally with just plain async functions, I don't see how
 we can catch this - the error happens when you return StopIteration from
 _any_ awaited function, you can't wrap around it to catch it instead.
 Given that views are always going to be async functions, unless we want to
 wrap every single view, decorator and middleware in our own custom Future
 it's not going to be reasonable to catch it.

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Ticket URL: 
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Re: [Django] #34998: Raising a StopIteration in asynchronous mode hangs the request

[Django]

#34998: Raising a StopIteration in asynchronous mode hangs the request
--+--
 Reporter:  Clément Escolano  |Owner:  nobody
 Type:  Uncategorized |   Status:  new
Component:  Uncategorized |  Version:  4.2
 Severity:  Normal|   Resolution:
 Keywords:| Triage Stage:  Unreviewed
Has patch:  0 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+--
Changes (by Carlton Gibson):

 * cc: Andrew Godwin (added)


Comment:

 Good issue. AFAICS this is https://github.com/python/cpython/issues/112182

 See also https://github.com/agronholm/anyio/pull/477 and
 https://github.com/tiangolo/fastapi/issues/966 — aynio was able to work
 around it, but it's not clear we're going to be able to doing anything
 pending a fix in asyncio.

 To quote Guido from the Python issue:

 > My first response is "don't do that". That's why it prints such an
 elaborate warning.

 Short of a concrete suggestion, 路‍♀️

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Re: [Django] #34998: Raising a StopIteration in asynchronous mode hangs the request

[Django]

#34998: Raising a StopIteration in asynchronous mode hangs the request
--+--
 Reporter:  Clément Escolano  |Owner:  nobody
 Type:  Uncategorized |   Status:  new
Component:  Uncategorized |  Version:  4.2
 Severity:  Normal|   Resolution:
 Keywords:| Triage Stage:  Unreviewed
Has patch:  0 |  Needs documentation:  0
  Needs tests:  0 |  Patch needs improvement:  0
Easy pickings:  0 |UI/UX:  0
--+--
Changes (by Mariusz Felisiak):

 * cc: Carlton Gibson (added)


Comment:

 Is it not a duplicate of #33795, #32798, or #33735?

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[Django] #34998: Raising a StopIteration in asynchronous mode hangs the request

[Django]

#34998: Raising a StopIteration in asynchronous mode hangs the request
+
   Reporter:  Clément Escolano  |  Owner:  nobody
   Type:  Uncategorized | Status:  new
  Component:  Uncategorized |Version:  4.2
   Severity:  Normal|   Keywords:
   Triage Stage:  Unreviewed|  Has patch:  0
Needs documentation:  0 |Needs tests:  0
Patch needs improvement:  0 |  Easy pickings:  0
  UI/UX:  0 |
+
 When using Django in Asynchronous mode, if some code raises a
 `StopIteration` error (generally when calling `next()` on an empty
 generator), the request hangs. I think Django should handle the error
 gracefully (display a 500 error page) instead.

 Basically, when the code raises a `StopIteration` error, the following is
 displayed and the request hangs:

 {{{
 TypeError: StopIteration interacts badly with generators and cannot be
 raised into a Future
 }}}

 I have reproduce the issue with a minimal project here: https://github.com
 /clement-escolano/django-stopiteration

 Relevant file is `stopiteration/views.py` which is a view called on
 `/error` endpoint and contains:

 {{{
 def error(request):
 next(i for i in [])
 return None
 }}}

 The Django application must be run with asynchronous support. For instance
 with: `uvicorn test_stopiteration.asgi:application`.

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Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

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