Replace all checks for isinstance(x, Future) with isfuture(x).

Author: gvanrossum

asyncio/base_events.py

@@ -363,7 +363,7 @@ def run_until_complete(self, future):
         """
         self._check_closed()
 
-        new_task = not isinstance(future, futures.Future)
+        new_task = not futures.isfuture(future)
         future = tasks.ensure_future(future, loop=self)
         if new_task:
             # An exception is raised if the future didn't complete, so there

asyncio/coroutines.py

@@ -204,8 +204,8 @@ def coroutine(func):
         @functools.wraps(func)
         def coro(*args, **kw):
             res = func(*args, **kw)
-            if isinstance(res, futures.Future) or inspect.isgenerator(res) or \
-                    isinstance(res, CoroWrapper):
+            if (futures.isfuture(res) or inspect.isgenerator(res) or
+                isinstance(res, CoroWrapper)):
                 res = yield from res
             elif _AwaitableABC is not None:
                 # If 'func' returns an Awaitable (new in 3.5) we

asyncio/futures.py

@@ -110,6 +110,16 @@ def __del__(self):
             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 getattr(obj, '_asyncio_future_blocking', None) is not None
+
+
 class Future:
     """This class is *almost* compatible with concurrent.futures.Future.
 
@@ -423,15 +433,17 @@ 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)
@@ -455,7 +467,7 @@ def _call_set_state(source):
 
 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)

asyncio/tasks.py

@@ -333,7 +333,7 @@ def wait(fs, *, loop=None, timeout=None, return_when=ALL_COMPLETED):
     Note: This does not raise TimeoutError! Futures that aren't done
     when the timeout occurs are returned in the second set.
     """
-    if isinstance(fs, futures.Future) or coroutines.iscoroutine(fs):
+    if futures.isfuture(fs) or coroutines.iscoroutine(fs):
         raise TypeError("expect a list of futures, not %s" % type(fs).__name__)
     if not fs:
         raise ValueError('Set of coroutines/Futures is empty.')
@@ -462,7 +462,7 @@ def as_completed(fs, *, loop=None, timeout=None):
 
     Note: The futures 'f' are not necessarily members of fs.
     """
-    if isinstance(fs, futures.Future) or coroutines.iscoroutine(fs):
+    if futures.isfuture(fs) or coroutines.iscoroutine(fs):
         raise TypeError("expect a list of futures, not %s" % type(fs).__name__)
     loop = loop if loop is not None else events.get_event_loop()
     todo = {ensure_future(f, loop=loop) for f in set(fs)}
@@ -538,7 +538,7 @@ def ensure_future(coro_or_future, *, loop=None):
 
     If the argument is a Future, it is returned directly.
     """
-    if isinstance(coro_or_future, futures.Future):
+    if futures.isfuture(coro_or_future):
         if loop is not None and loop is not coro_or_future._loop:
             raise ValueError('loop argument must agree with Future')
         return coro_or_future
@@ -614,7 +614,7 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
 
     arg_to_fut = {}
     for arg in set(coros_or_futures):
-        if not isinstance(arg, futures.Future):
+        if not futures.isfuture(arg):
             fut = ensure_future(arg, loop=loop)
             if loop is None:
                 loop = fut._loop