Run all error callbacks that have been added to this Deferred.

Each callback will have its result passed as the first argument to the next; this way, the callbacks act as a 'processing chain'. Also, if the error-callback returns a non-Failure or doesn't raise an Exception, processing will continue on the *success*-callback chain.

If the argument that's passed to me is not a failure.Failure instance, it will be embedded in one. If no argument is passed, a failure.Failure instance will be created based on the current traceback stack.

Passing a string as `fail' is deprecated, and will be punished with a warning message.

An instance of Deferred may only have either callback or errback called on it, and only once.

ParametersfailThe Failure object which will be passed to the first errback added to this Deferred (via addErrback). Alternatively, a Exception instance from which a Failure will be constructed (with no traceback) or None to create a Failure instance from the current exception state (with a traceback).
RaisesAlreadyCalledErrorIf callback or errback has already been called on this Deferred.
NoCurrentExceptionErrorIf fail is None but there is no current exception state.
API Documentation for Twisted, generated by pydoctor at 2015-05-24 20:04:00.