from twisted.internet import defer

def c(res):
    print "HELLO!"
    raise Exception()
    return 2

def f(_):
    print "HANDLED!"
    return _

def end(_):
    print "END!"
    return _.value

def new_f(_):
    print "HANDLED 2!"
    return _

def a():
    l = defer.Deferred()
    l.addCallbacks(c, new_f)
    d = defer.Deferred()
    d.addCallback(c)
    d.addErrback(f)
    #if you comment this line all works as expected
    d.chainDeferred(l)
    d.addErrback(end)
    return d

a().callback(2)