[Twisted-Python] Catching all the exceptions in a Twisted program

[Facundo Batista]

Hello!

I've just subscribed to the list, but I'm using Twisted from a while ago.

I need to do something, and wasn't able to find out how to do it.  Well, I
*did* find out, but it's a horrible hack, and actually depends on something
that may be a bug, so it's worth asking here about this :)

In a project I'm doing [0], I want to catch all problems (unhandled
exceptions), log them and show them in stderr after a bit massaging.  My
first approach was to hook me in sys.excepthook, and it worked on some
cases.  But I saw some cases where it didn't [1].

Specifically, when the exception was inside a deferred, it didn't call
excepthook.  Why not? I started to check the code, and found the following
snippet, at the end of Deferred._run_callbacks, in defer.py:

   if isinstance(self.result, failure.Failure):
       self.result.cleanFailure()
       if self._debugInfo is None:
           self._debugInfo = DebugInfo()
       self._debugInfo.failResult = self.result

>From this, I have two questions:

1. The rest of the code only instantiates and uses DebugInfo
   "if self.debug".  Why this part of the code doesn't care about the
   self.debug flag and always uses it?  Is it intended and DebugInfo()
   not being used for debug is a misname left there for historical
   reasons?  Should I open a bug about this?

2. I did the following (ugly) hack to achieve my results:

    import twisted.internet.defer

    # ugliest thing I saw in a *long* time
    class MyDebugInfo(object):

        def _error_happened(self, failure):
            msg = failure.getTraceback()
            _expose_exception(msg)

        failResult = property(fset=_error_happened)

    twisted.internet.defer.DebugInfo = MyDebugInfo

   Is there a better way to do this?  Actually, this is working correctly,
   but I don't know if it's the right way to do it, and don't want to
   depend of DebugInfo() being called always in this case.

Thank you very much!

[0] http://launchpad.net/magicicada
[1] http://bugs.launchpad.net/magicicada/+bug/665681

-- 
.    Facundo

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