"""Tests for futures.py.""" import concurrent.futures import gc import re import sys import threading import unittest from unittest import mock from types import GenericAlias import asyncio from asyncio import futures from test.test_asyncio import utils as test_utils from test import support def tearDownModule(): asyncio.set_event_loop_policy(None) def _fakefunc(f): return f def first_cb(): pass def last_cb(): pass class DuckFuture: # Class that does not inherit from Future but aims to be duck-type # compatible with it. _asyncio_future_blocking = False __cancelled = False __result = None __exception = None def cancel(self): if self.done(): return False self.__cancelled = True return True def cancelled(self): return self.__cancelled def done(self): return (self.__cancelled or self.__result is not None or self.__exception is not None) def result(self): self.assertFalse(self.cancelled()) if self.__exception is not None: raise self.__exception return self.__result def exception(self): self.assertFalse(self.cancelled()) return self.__exception def set_result(self, result): self.assertFalse(self.done()) self.assertIsNotNone(result) self.__result = result def set_exception(self, exception): self.assertFalse(self.done()) self.assertIsNotNone(exception) self.__exception = exception def __iter__(self): if not self.done(): self._asyncio_future_blocking = True yield self self.assertTrue(self.done()) return self.result() class DuckTests(test_utils.TestCase): def setUp(self): super().setUp() self.loop = self.new_test_loop() self.addCleanup(self.loop.close) def test_wrap_future(self): f = DuckFuture() g = asyncio.wrap_future(f) self.assertIs(g, f) def test_ensure_future(self): f = DuckFuture() g = asyncio.ensure_future(f) self.assertIs(g, f) class BaseFutureTests: def _new_future(self, *args, **kwargs): return self.cls(*args, **kwargs) def setUp(self): super().setUp() self.loop = self.new_test_loop() self.addCleanup(self.loop.close) def test_generic_alias(self): future = self.cls[str] self.assertEqual(future.__args__, (str,)) self.assertIsInstance(future, GenericAlias) def test_isfuture(self): class MyFuture: _asyncio_future_blocking = None def __init__(self): self._asyncio_future_blocking = False self.assertFalse(asyncio.isfuture(MyFuture)) self.assertTrue(asyncio.isfuture(MyFuture())) self.assertFalse(asyncio.isfuture(1)) # As `isinstance(Mock(), Future)` returns `False` self.assertFalse(asyncio.isfuture(mock.Mock())) f = self._new_future(loop=self.loop) self.assertTrue(asyncio.isfuture(f)) self.assertFalse(asyncio.isfuture(type(f))) # As `isinstance(Mock(Future), Future)` returns `True` self.assertTrue(asyncio.isfuture(mock.Mock(type(f)))) f.cancel() def test_initial_state(self): f = self._new_future(loop=self.loop) self.assertFalse(f.cancelled()) self.assertFalse(f.done()) f.cancel() self.assertTrue(f.cancelled()) def test_constructor_without_loop(self): with self.assertWarns(DeprecationWarning) as cm: with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'): self._new_future() self.assertEqual(cm.filename, __file__) def test_constructor_use_running_loop(self): async def test(): return self._new_future() f = self.loop.run_until_complete(test()) self.assertIs(f._loop, self.loop) self.assertIs(f.get_loop(), self.loop) def test_constructor_use_global_loop(self): # Deprecated in 3.10 asyncio.set_event_loop(self.loop) self.addCleanup(asyncio.set_event_loop, None) with self.assertWarns(DeprecationWarning) as cm: f = self._new_future() self.assertEqual(cm.filename, __file__) self.assertIs(f._loop, self.loop) self.assertIs(f.get_loop(), self.loop) def test_constructor_positional(self): # Make sure Future doesn't accept a positional argument self.assertRaises(TypeError, self._new_future, 42) def test_uninitialized(self): # Test that C Future doesn't crash when Future.__init__() # call was skipped. fut = self.cls.__new__(self.cls, loop=self.loop) self.assertRaises(asyncio.InvalidStateError, fut.result) fut = self.cls.__new__(self.cls, loop=self.loop) self.assertRaises(asyncio.InvalidStateError, fut.exception) fut = self.cls.__new__(self.cls, loop=self.loop) with self.assertRaises((RuntimeError, AttributeError)): fut.set_result(None) fut = self.cls.__new__(self.cls, loop=self.loop) with self.assertRaises((RuntimeError, AttributeError)): fut.set_exception(Exception) fut = self.cls.__new__(self.cls, loop=self.loop) with self.assertRaises((RuntimeError, AttributeError)): fut.cancel() fut = self.cls.__new__(self.cls, loop=self.loop) with self.assertRaises((RuntimeError, AttributeError)): fut.add_done_callback(lambda f: None) fut = self.cls.__new__(self.cls, loop=self.loop) with self.assertRaises((RuntimeError, AttributeError)): fut.remove_done_callback(lambda f: None) fut = self.cls.__new__(self.cls, loop=self.loop) try: repr(fut) except (RuntimeError, AttributeError): pass fut = self.cls.__new__(self.cls, loop=self.loop) try: fut.__await__() except RuntimeError: pass fut = self.cls.__new__(self.cls, loop=self.loop) try: iter(fut) except RuntimeError: pass fut = self.cls.__new__(self.cls, loop=self.loop) self.assertFalse(fut.cancelled()) self.assertFalse(fut.done()) def test_future_cancel_message_getter(self): f = self._new_future(loop=self.loop) self.assertTrue(hasattr(f, '_cancel_message')) self.assertEqual(f._cancel_message, None) with self.assertWarnsRegex( DeprecationWarning, "Passing 'msg' argument" ): f.cancel('my message') with self.assertRaises(asyncio.CancelledError): self.loop.run_until_complete(f) self.assertEqual(f._cancel_message, 'my message') def test_future_cancel_message_setter(self): f = self._new_future(loop=self.loop) with self.assertWarnsRegex( DeprecationWarning, "Passing 'msg' argument" ): f.cancel('my message') f._cancel_message = 'my new message' self.assertEqual(f._cancel_message, 'my new message') # Also check that the value is used for cancel(). with self.assertRaises(asyncio.CancelledError): self.loop.run_until_complete(f) self.assertEqual(f._cancel_message, 'my new message') def test_cancel(self): f = self._new_future(loop=self.loop) self.assertTrue(f.cancel()) self.assertTrue(f.cancelled()) self.assertTrue(f.done()) self.assertRaises(asyncio.CancelledError, f.result) self.assertRaises(asyncio.CancelledError, f.exception) self.assertRaises(asyncio.InvalidStateError, f.set_result, None) self.assertRaises(asyncio.InvalidStateError, f.set_exception, None) self.assertFalse(f.cancel()) def test_result(self): f = self._new_future(loop=self.loop) self.assertRaises(asyncio.InvalidStateError, f.result) f.set_result(42) self.assertFalse(f.cancelled()) self.assertTrue(f.done()) self.assertEqual(f.result(), 42) self.assertEqual(f.exception(), None) self.assertRaises(asyncio.InvalidStateError, f.set_result, None) self.assertRaises(asyncio.InvalidStateError, f.set_exception, None) self.assertFalse(f.cancel()) def test_exception(self): exc = RuntimeError() f = self._new_future(loop=self.loop) self.assertRaises(asyncio.InvalidStateError, f.exception) # StopIteration cannot be raised into a Future - CPython issue26221 self.assertRaisesRegex(TypeError, "StopIteration .* cannot be raised", f.set_exception, StopIteration) f.set_exception(exc) self.assertFalse(f.cancelled()) self.assertTrue(f.done()) self.assertRaises(RuntimeError, f.result) self.assertEqual(f.exception(), exc) self.assertRaises(asyncio.InvalidStateError, f.set_result, None) self.assertRaises(asyncio.InvalidStateError, f.set_exception, None) self.assertFalse(f.cancel()) def test_exception_class(self): f = self._new_future(loop=self.loop) f.set_exception(RuntimeError) self.assertIsInstance(f.exception(), RuntimeError) def test_yield_from_twice(self): f = self._new_future(loop=self.loop) def fixture(): yield 'A' x = yield from f yield 'B', x y = yield from f yield 'C', y g = fixture() self.assertEqual(next(g), 'A') # yield 'A'. self.assertEqual(next(g), f) # First yield from f. f.set_result(42) self.assertEqual(next(g), ('B', 42)) # yield 'B', x. # The second "yield from f" does not yield f. self.assertEqual(next(g), ('C', 42)) # yield 'C', y. def test_future_repr(self): self.loop.set_debug(True) f_pending_debug = self._new_future(loop=self.loop) frame = f_pending_debug._source_traceback[-1] self.assertEqual( repr(f_pending_debug), f'<{self.cls.__name__} pending created at {frame[0]}:{frame[1]}>') f_pending_debug.cancel() self.loop.set_debug(False) f_pending = self._new_future(loop=self.loop) self.assertEqual(repr(f_pending), f'<{self.cls.__name__} pending>') f_pending.cancel() f_cancelled = self._new_future(loop=self.loop) f_cancelled.cancel() self.assertEqual(repr(f_cancelled), f'<{self.cls.__name__} cancelled>') f_result = self._new_future(loop=self.loop) f_result.set_result(4) self.assertEqual( repr(f_result), f'<{self.cls.__name__} finished result=4>') self.assertEqual(f_result.result(), 4) exc = RuntimeError() f_exception = self._new_future(loop=self.loop) f_exception.set_exception(exc) self.assertEqual( repr(f_exception), f'<{self.cls.__name__} finished exception=RuntimeError()>') self.assertIs(f_exception.exception(), exc) def func_repr(func): filename, lineno = test_utils.get_function_source(func) text = '%s() at %s:%s' % (func.__qualname__, filename, lineno) return re.escape(text) f_one_callbacks = self._new_future(loop=self.loop) f_one_callbacks.add_done_callback(_fakefunc) fake_repr = func_repr(_fakefunc) self.assertRegex( repr(f_one_callbacks), r'<' + self.cls.__name__ + r' pending cb=\[%s\]>' % fake_repr) f_one_callbacks.cancel() self.assertEqual(repr(f_one_callbacks), f'<{self.cls.__name__} cancelled>') f_two_callbacks = self._new_future(loop=self.loop) f_two_callbacks.add_done_callback(first_cb) f_two_callbacks.add_done_callback(last_cb) first_repr = func_repr(first_cb) last_repr = func_repr(last_cb) self.assertRegex(repr(f_two_callbacks), r'<' + self.cls.__name__ + r' pending cb=\[%s, %s\]>' % (first_repr, last_repr)) f_many_callbacks = self._new_future(loop=self.loop) f_many_callbacks.add_done_callback(first_cb) for i in range(8): f_many_callbacks.add_done_callback(_fakefunc) f_many_callbacks.add_done_callback(last_cb) cb_regex = r'%s, <8 more>, %s' % (first_repr, last_repr) self.assertRegex( repr(f_many_callbacks), r'<' + self.cls.__name__ + r' pending cb=\[%s\]>' % cb_regex) f_many_callbacks.cancel() self.assertEqual(repr(f_many_callbacks), f'<{self.cls.__name__} cancelled>') def test_copy_state(self): from asyncio.futures import _copy_future_state f = self._new_future(loop=self.loop) f.set_result(10) newf = self._new_future(loop=self.loop) _copy_future_state(f, newf) self.assertTrue(newf.done()) self.assertEqual(newf.result(), 10) f_exception = self._new_future(loop=self.loop) f_exception.set_exception(RuntimeError()) newf_exception = self._new_future(loop=self.loop) _copy_future_state(f_exception, newf_exception) self.assertTrue(newf_exception.done()) self.assertRaises(RuntimeError, newf_exception.result) f_cancelled = self._new_future(loop=self.loop) f_cancelled.cancel() newf_cancelled = self._new_future(loop=self.loop) _copy_future_state(f_cancelled, newf_cancelled) self.assertTrue(newf_cancelled.cancelled()) def test_iter(self): fut = self._new_future(loop=self.loop) def coro(): yield from fut def test(): arg1, arg2 = coro() with self.assertRaisesRegex(RuntimeError, "await wasn't used"): test() fut.cancel() def test_log_traceback(self): fut = self._new_future(loop=self.loop) with self.assertRaisesRegex(ValueError, 'can only be set to False'): fut._log_traceback = True @mock.patch('asyncio.base_events.logger') def test_tb_logger_abandoned(self, m_log): fut = self._new_future(loop=self.loop) del fut self.assertFalse(m_log.error.called) @mock.patch('asyncio.base_events.logger') def test_tb_logger_not_called_after_cancel(self, m_log): fut = self._new_future(loop=self.loop) fut.set_exception(Exception()) fut.cancel() del fut self.assertFalse(m_log.error.called) @mock.patch('asyncio.base_events.logger') def test_tb_logger_result_unretrieved(self, m_log): fut = self._new_future(loop=self.loop) fut.set_result(42) del fut self.assertFalse(m_log.error.called) @mock.patch('asyncio.base_events.logger') def test_tb_logger_result_retrieved(self, m_log): fut = self._new_future(loop=self.loop) fut.set_result(42) fut.result() del fut self.assertFalse(m_log.error.called) @mock.patch('asyncio.base_events.logger') def test_tb_logger_exception_unretrieved(self, m_log): fut = self._new_future(loop=self.loop) fut.set_exception(RuntimeError('boom')) del fut test_utils.run_briefly(self.loop) support.gc_collect() self.assertTrue(m_log.error.called) @mock.patch('asyncio.base_events.logger') def test_tb_logger_exception_retrieved(self, m_log): fut = self._new_future(loop=self.loop) fut.set_exception(RuntimeError('boom')) fut.exception() del fut self.assertFalse(m_log.error.called) @mock.patch('asyncio.base_events.logger') def test_tb_logger_exception_result_retrieved(self, m_log): fut = self._new_future(loop=self.loop) fut.set_exception(RuntimeError('boom')) self.assertRaises(RuntimeError, fut.result) del fut self.assertFalse(m_log.error.called) def test_wrap_future(self): def run(arg): return (arg, threading.get_ident()) ex = concurrent.futures.ThreadPoolExecutor(1) f1 = ex.submit(run, 'oi') f2 = asyncio.wrap_future(f1, loop=self.loop) res, ident = self.loop.run_until_complete(f2) self.assertTrue(asyncio.isfuture(f2)) self.assertEqual(res, 'oi') self.assertNotEqual(ident, threading.get_ident()) ex.shutdown(wait=True) def test_wrap_future_future(self): f1 = self._new_future(loop=self.loop) f2 = asyncio.wrap_future(f1) self.assertIs(f1, f2) def test_wrap_future_without_loop(self): def run(arg): return (arg, threading.get_ident()) ex = concurrent.futures.ThreadPoolExecutor(1) f1 = ex.submit(run, 'oi') with self.assertWarns(DeprecationWarning) as cm: with self.assertRaises(RuntimeError): asyncio.wrap_future(f1) self.assertEqual(cm.filename, __file__) ex.shutdown(wait=True) def test_wrap_future_use_running_loop(self): def run(arg): return (arg, threading.get_ident()) ex = concurrent.futures.ThreadPoolExecutor(1) f1 = ex.submit(run, 'oi') async def test(): return asyncio.wrap_future(f1) f2 = self.loop.run_until_complete(test()) self.assertIs(self.loop, f2._loop) ex.shutdown(wait=True) def test_wrap_future_use_global_loop(self): # Deprecated in 3.10 asyncio.set_event_loop(self.loop) self.addCleanup(asyncio.set_event_loop, None) def run(arg): return (arg, threading.get_ident()) ex = concurrent.futures.ThreadPoolExecutor(1) f1 = ex.submit(run, 'oi') with self.assertWarns(DeprecationWarning) as cm: f2 = asyncio.wrap_future(f1) self.assertEqual(cm.filename, __file__) self.assertIs(self.loop, f2._loop) ex.shutdown(wait=True) def test_wrap_future_cancel(self): f1 = concurrent.futures.Future() f2 = asyncio.wrap_future(f1, loop=self.loop) f2.cancel() test_utils.run_briefly(self.loop) self.assertTrue(f1.cancelled()) self.assertTrue(f2.cancelled()) def test_wrap_future_cancel2(self): f1 = concurrent.futures.Future() f2 = asyncio.wrap_future(f1, loop=self.loop) f1.set_result(42) f2.cancel() test_utils.run_briefly(self.loop) self.assertFalse(f1.cancelled()) self.assertEqual(f1.result(), 42) self.assertTrue(f2.cancelled()) def test_future_source_traceback(self): self.loop.set_debug(True) future = self._new_future(loop=self.loop) lineno = sys._getframe().f_lineno - 1 self.assertIsInstance(future._source_traceback, list) self.assertEqual(future._source_traceback[-2][:3], (__file__, lineno, 'test_future_source_traceback')) @mock.patch('asyncio.base_events.logger') def check_future_exception_never_retrieved(self, debug, m_log): self.loop.set_debug(debug) def memory_error(): try: raise MemoryError() except BaseException as exc: return exc exc = memory_error() future = self._new_future(loop=self.loop) future.set_exception(exc) future = None test_utils.run_briefly(self.loop) support.gc_collect() regex = f'^{self.cls.__name__} exception was never retrieved\n' exc_info = (type(exc), exc, exc.__traceback__) m_log.error.assert_called_once_with(mock.ANY, exc_info=exc_info) message = m_log.error.call_args[0][0] self.assertRegex(message, re.compile(regex, re.DOTALL)) def test_future_exception_never_retrieved(self): self.check_future_exception_never_retrieved(False) def test_future_exception_never_retrieved_debug(self): self.check_future_exception_never_retrieved(True) def test_set_result_unless_cancelled(self): fut = self._new_future(loop=self.loop) fut.cancel() futures._set_result_unless_cancelled(fut, 2) self.assertTrue(fut.cancelled()) def test_future_stop_iteration_args(self): fut = self._new_future(loop=self.loop) fut.set_result((1, 2)) fi = fut.__iter__() result = None try: fi.send(None) except StopIteration as ex: result = ex.args[0] else: self.fail('StopIteration was expected') self.assertEqual(result, (1, 2)) def test_future_iter_throw(self): fut = self._new_future(loop=self.loop) fi = iter(fut) self.assertRaises(TypeError, fi.throw, Exception, Exception("elephant"), 32) self.assertRaises(TypeError, fi.throw, Exception("elephant"), Exception("elephant")) self.assertRaises(TypeError, fi.throw, list) def test_future_del_collect(self): class Evil: def __del__(self): gc.collect() for i in range(100): fut = self._new_future(loop=self.loop) fut.set_result(Evil()) @unittest.skipUnless(hasattr(futures, '_CFuture'), 'requires the C _asyncio module') class CFutureTests(BaseFutureTests, test_utils.TestCase): try: cls = futures._CFuture except AttributeError: cls = None def test_future_del_segfault(self): fut = self._new_future(loop=self.loop) with self.assertRaises(AttributeError): del fut._asyncio_future_blocking with self.assertRaises(AttributeError): del fut._log_traceback @unittest.skipUnless(hasattr(futures, '_CFuture'), 'requires the C _asyncio module') class CSubFutureTests(BaseFutureTests, test_utils.TestCase): try: class CSubFuture(futures._CFuture): pass cls = CSubFuture except AttributeError: cls = None class PyFutureTests(BaseFutureTests, test_utils.TestCase): cls = futures._PyFuture class BaseFutureDoneCallbackTests(): def setUp(self): super().setUp() self.loop = self.new_test_loop() def run_briefly(self): test_utils.run_briefly(self.loop) def _make_callback(self, bag, thing): # Create a callback function that appends thing to bag. def bag_appender(future): bag.append(thing) return bag_appender def _new_future(self): raise NotImplementedError def test_callbacks_remove_first_callback(self): bag = [] f = self._new_future() cb1 = self._make_callback(bag, 42) cb2 = self._make_callback(bag, 17) cb3 = self._make_callback(bag, 100) f.add_done_callback(cb1) f.add_done_callback(cb2) f.add_done_callback(cb3) f.remove_done_callback(cb1) f.remove_done_callback(cb1) self.assertEqual(bag, []) f.set_result('foo') self.run_briefly() self.assertEqual(bag, [17, 100]) self.assertEqual(f.result(), 'foo') def test_callbacks_remove_first_and_second_callback(self): bag = [] f = self._new_future() cb1 = self._make_callback(bag, 42) cb2 = self._make_callback(bag, 17) cb3 = self._make_callback(bag, 100) f.add_done_callback(cb1) f.add_done_callback(cb2) f.add_done_callback(cb3) f.remove_done_callback(cb1) f.remove_done_callback(cb2) f.remove_done_callback(cb1) self.assertEqual(bag, []) f.set_result('foo') self.run_briefly() self.assertEqual(bag, [100]) self.assertEqual(f.result(), 'foo') def test_callbacks_remove_third_callback(self): bag = [] f = self._new_future() cb1 = self._make_callback(bag, 42) cb2 = self._make_callback(bag, 17) cb3 = self._make_callback(bag, 100) f.add_done_callback(cb1) f.add_done_callback(cb2) f.add_done_callback(cb3) f.remove_done_callback(cb3) f.remove_done_callback(cb3) self.assertEqual(bag, []) f.set_result('foo') self.run_briefly() self.assertEqual(bag, [42, 17]) self.assertEqual(f.result(), 'foo') def test_callbacks_invoked_on_set_result(self): bag = [] f = self._new_future() f.add_done_callback(self._make_callback(bag, 42)) f.add_done_callback(self._make_callback(bag, 17)) self.assertEqual(bag, []) f.set_result('foo') self.run_briefly() self.assertEqual(bag, [42, 17]) self.assertEqual(f.result(), 'foo') def test_callbacks_invoked_on_set_exception(self): bag = [] f = self._new_future() f.add_done_callback(self._make_callback(bag, 100)) self.assertEqual(bag, []) exc = RuntimeError() f.set_exception(exc) self.run_briefly() self.assertEqual(bag, [100]) self.assertEqual(f.exception(), exc) def test_remove_done_callback(self): bag = [] f = self._new_future() cb1 = self._make_callback(bag, 1) cb2 = self._make_callback(bag, 2) cb3 = self._make_callback(bag, 3) # Add one cb1 and one cb2. f.add_done_callback(cb1) f.add_done_callback(cb2) # One instance of cb2 removed. Now there's only one cb1. self.assertEqual(f.remove_done_callback(cb2), 1) # Never had any cb3 in there. self.assertEqual(f.remove_done_callback(cb3), 0) # After this there will be 6 instances of cb1 and one of cb2. f.add_done_callback(cb2) for i in range(5): f.add_done_callback(cb1) # Remove all instances of cb1. One cb2 remains. self.assertEqual(f.remove_done_callback(cb1), 6) self.assertEqual(bag, []) f.set_result('foo') self.run_briefly() self.assertEqual(bag, [2]) self.assertEqual(f.result(), 'foo') def test_remove_done_callbacks_list_mutation(self): # see http://bugs.python.org/issue28963 for details fut = self._new_future() fut.add_done_callback(str) for _ in range(63): fut.add_done_callback(id) class evil: def __eq__(self, other): fut.remove_done_callback(id) return False fut.remove_done_callback(evil()) def test_schedule_callbacks_list_mutation_1(self): # see http://bugs.python.org/issue28963 for details def mut(f): f.remove_done_callback(str) fut = self._new_future() fut.add_done_callback(mut) fut.add_done_callback(str) fut.add_done_callback(str) fut.set_result(1) test_utils.run_briefly(self.loop) def test_schedule_callbacks_list_mutation_2(self): # see http://bugs.python.org/issue30828 for details fut = self._new_future() fut.add_done_callback(str) for _ in range(63): fut.add_done_callback(id) max_extra_cbs = 100 extra_cbs = 0 class evil: def __eq__(self, other): nonlocal extra_cbs extra_cbs += 1 if extra_cbs < max_extra_cbs: fut.add_done_callback(id) return False fut.remove_done_callback(evil()) @unittest.skipUnless(hasattr(futures, '_CFuture'), 'requires the C _asyncio module') class CFutureDoneCallbackTests(BaseFutureDoneCallbackTests, test_utils.TestCase): def _new_future(self): return futures._CFuture(loop=self.loop) @unittest.skipUnless(hasattr(futures, '_CFuture'), 'requires the C _asyncio module') class CSubFutureDoneCallbackTests(BaseFutureDoneCallbackTests, test_utils.TestCase): def _new_future(self): class CSubFuture(futures._CFuture): pass return CSubFuture(loop=self.loop) class PyFutureDoneCallbackTests(BaseFutureDoneCallbackTests, test_utils.TestCase): def _new_future(self): return futures._PyFuture(loop=self.loop) class BaseFutureInheritanceTests: def _get_future_cls(self): raise NotImplementedError def setUp(self): super().setUp() self.loop = self.new_test_loop() self.addCleanup(self.loop.close) def test_inherit_without_calling_super_init(self): # See https://bugs.python.org/issue38785 for the context cls = self._get_future_cls() class MyFut(cls): def __init__(self, *args, **kwargs): # don't call super().__init__() pass fut = MyFut(loop=self.loop) with self.assertRaisesRegex( RuntimeError, "Future object is not initialized." ): fut.get_loop() class PyFutureInheritanceTests(BaseFutureInheritanceTests, test_utils.TestCase): def _get_future_cls(self): return futures._PyFuture @unittest.skipUnless(hasattr(futures, '_CFuture'), 'requires the C _asyncio module') class CFutureInheritanceTests(BaseFutureInheritanceTests, test_utils.TestCase): def _get_future_cls(self): return futures._CFuture if __name__ == '__main__': unittest.main()