def on_completed():
nonlocal last_value
if has_value:
future.set_result(last_value)
else:
future.set_exception(SequenceContainsNoElementsError())
last_value = None
def on_completed():
if not seen_value[0] and not has_default:
observer.on_error(SequenceContainsNoElementsError())
else:
observer.on_next(value[0])
observer.on_completed()
def first_only(x):
if not len(x):
raise SequenceContainsNoElementsError()
return x[0]
def first_only(x: Sequence) -> Any:
if not x:
raise SequenceContainsNoElementsError()
return x[0]