Here's code that generates an error on line #9 in f1() 1 import time, sys 2 from twisted.internet import reactor 3 from twisted.internet.task import deferLater 4 from twisted.internet.defer import inlineCallbacks 5 6 @inlineCallbacks 7 def f1(): 8 yield time.time() 9 {'a': 'A', 'b': 'B'}['c'] # KeyError 10 11 @inlineCallbacks 12 def f2(): 13 yield f1() 14 15 def on_err(failure): 16 print("on_err: ===>", failure.getErrorMessage()) 17 failure.printTraceback(file=sys.stderr) 18 if reactor.running: 19 reactor.stop() 20 21 def done(*args, **kargs): 22 print("done.") 23 reactor.stop() 24 25 deferLater(reactor, 0, f2).addCallback(done).addErrback(on_err) 26 reactor.run() running w/ python 2.7 outputs this: --- <exception caught here> --- File ".....\lib\site-packages\twisted\internet\defer.py", line 1128, in _inlineCallbacks result = g.send(result) File "../temp/tb.py", line 9, in f1 {'a': 'A', 'b': 'B'}['c'] exceptions.KeyError: 'c' python 3.6.1 (twisted 17.5.0) outputs this: File ".....\lib\site-packages\twisted\internet\defer.py", line 1299, in _inlineCallbacks result = result.throwExceptionIntoGenerator(g) File ".....\lib\site-packages\twisted\python\failure.py", line 393, in throwExceptionIntoGenerator return g.throw(self.type, self.value, self.tb) File "../temp/tb.py", line 13, in f2 yield f1() builtins.KeyError: 'c' I can know there is a failure in f1() but line and other specifics are dropped changing line #25 to call f1() gives a better message, so it's something related to stack frame. Is there any way (aside from adding logging at each level to internet/defer.py:_inlineCallbacks) to get a better error message in py3? thank you - Aaron