diff options
Diffstat (limited to 'Lib/asyncio/futures.py')
| -rw-r--r-- | Lib/asyncio/futures.py | 48 |
1 files changed, 37 insertions, 11 deletions
diff --git a/Lib/asyncio/futures.py b/Lib/asyncio/futures.py index 4dcb654..9ca8d84 100644 --- a/Lib/asyncio/futures.py +++ b/Lib/asyncio/futures.py @@ -2,7 +2,7 @@ __all__ = ['CancelledError', 'TimeoutError', 'InvalidStateError', - 'Future', 'wrap_future', + 'Future', 'wrap_future', 'isfuture', ] import concurrent.futures._base @@ -110,6 +110,17 @@ class _TracebackLogger: self.loop.call_exception_handler({'message': msg}) +def isfuture(obj): + """Check for a Future. + + This returns True when obj is a Future instance or is advertising + itself as duck-type compatible by setting _asyncio_future_blocking. + See comment in Future for more details. + """ + return (hasattr(obj.__class__, '_asyncio_future_blocking') and + obj._asyncio_future_blocking is not None) + + class Future: """This class is *almost* compatible with concurrent.futures.Future. @@ -134,7 +145,15 @@ class Future: _loop = None _source_traceback = None - _blocking = False # proper use of future (yield vs yield from) + # This field is used for a dual purpose: + # - Its presence is a marker to declare that a class implements + # the Future protocol (i.e. is intended to be duck-type compatible). + # The value must also be not-None, to enable a subclass to declare + # that it is not compatible by setting this to None. + # - It is set by __iter__() below so that Task._step() can tell + # the difference between `yield from Future()` (correct) vs. + # `yield Future()` (incorrect). + _asyncio_future_blocking = False _log_traceback = False # Used for Python 3.4 and later _tb_logger = None # Used for Python 3.3 only @@ -142,7 +161,7 @@ class Future: def __init__(self, *, loop=None): """Initialize the future. - The optional event_loop argument allows to explicitly set the event + The optional event_loop argument allows explicitly setting the event loop object used by the future. If it's not provided, the future uses the default event loop. """ @@ -341,6 +360,9 @@ class Future: raise InvalidStateError('{}: {!r}'.format(self._state, self)) if isinstance(exception, type): exception = exception() + if type(exception) is StopIteration: + raise TypeError("StopIteration interacts badly with generators " + "and cannot be raised into a Future") self._exception = exception self._state = _FINISHED self._schedule_callbacks() @@ -354,7 +376,7 @@ class Future: def __iter__(self): if not self.done(): - self._blocking = True + self._asyncio_future_blocking = True yield self # This tells Task to wait for completion. assert self.done(), "yield from wasn't used with future" return self.result() # May raise too. @@ -412,15 +434,17 @@ def _chain_future(source, destination): If destination is cancelled, source gets cancelled too. Compatible with both asyncio.Future and concurrent.futures.Future. """ - if not isinstance(source, (Future, concurrent.futures.Future)): + if not isfuture(source) and not isinstance(source, + concurrent.futures.Future): raise TypeError('A future is required for source argument') - if not isinstance(destination, (Future, concurrent.futures.Future)): + if not isfuture(destination) and not isinstance(destination, + concurrent.futures.Future): raise TypeError('A future is required for destination argument') - source_loop = source._loop if isinstance(source, Future) else None - dest_loop = destination._loop if isinstance(destination, Future) else None + source_loop = source._loop if isfuture(source) else None + dest_loop = destination._loop if isfuture(destination) else None def _set_state(future, other): - if isinstance(future, Future): + if isfuture(future): _copy_future_state(other, future) else: _set_concurrent_future_state(future, other) @@ -444,10 +468,12 @@ def _chain_future(source, destination): def wrap_future(future, *, loop=None): """Wrap concurrent.futures.Future object.""" - if isinstance(future, Future): + if isfuture(future): return future assert isinstance(future, concurrent.futures.Future), \ 'concurrent.futures.Future is expected, got {!r}'.format(future) - new_future = Future(loop=loop) + if loop is None: + loop = events.get_event_loop() + new_future = loop.create_future() _chain_future(future, new_future) return new_future |