Rename Future._blocking to _asyncio_future_blocking.

This is now an official "protected" API that can be used to write
classes that are duck-type-compatible with Future without subclassing
it.  (For that purpose I also changed isinstance(result, Future) to
check for this attribute instead.)

Hopefully Amber Brown can use this to make Twisted.Deferred compatible
with asyncio.Future.

Tests and docs are TBD.

1 files changed, 4 insertions, 3 deletions

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 0cca8e36a5..3e200f6338 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -249,7 +249,8 @@ class Task(futures.Future):
             self.set_exception(exc)
             raise
         else:
-            if isinstance(result, futures.Future):
+            blocking = getattr(result, '_asyncio_future_blocking', None)
+            if blocking is not None:
                 # Yielded Future must come from Future.__iter__().
                 if result._loop is not self._loop:
                     self._loop.call_soon(
@@ -257,8 +258,8 @@ class Task(futures.Future):
                         RuntimeError(
                             'Task {!r} got Future {!r} attached to a '
                             'different loop'.format(self, result)))
-                elif result._blocking:
-                    result._blocking = False
+                elif blocking:
+                    result._asyncio_future_blocking = False
                     result.add_done_callback(self._wakeup)
                     self._fut_waiter = result
                     if self._must_cancel: