1 files changed, 71 insertions, 0 deletions
diff --git a/Lib/asyncio/base_futures.py b/Lib/asyncio/base_futures.py
new file mode 100644
index 0000000000..01259a062e
--- /dev/null
+++ b/Lib/asyncio/base_futures.py
@@ -0,0 +1,71 @@
+__all__ = []
+
+import concurrent.futures._base
+import reprlib
+
+from . import events
+
+Error = concurrent.futures._base.Error
+CancelledError = concurrent.futures.CancelledError
+TimeoutError = concurrent.futures.TimeoutError
+
+
+class InvalidStateError(Error):
+    """The operation is not allowed in this state."""
+
+
+# States for Future.
+_PENDING = 'PENDING'
+_CANCELLED = 'CANCELLED'
+_FINISHED = 'FINISHED'
+
+
+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)
+
+
+def _format_callbacks(cb):
+    """helper function for Future.__repr__"""
+    size = len(cb)
+    if not size:
+        cb = ''
+
+    def format_cb(callback):
+        return events._format_callback_source(callback, ())
+
+    if size == 1:
+        cb = format_cb(cb[0])
+    elif size == 2:
+        cb = '{}, {}'.format(format_cb(cb[0]), format_cb(cb[1]))
+    elif size > 2:
+        cb = '{}, <{} more>, {}'.format(format_cb(cb[0]),
+                                        size - 2,
+                                        format_cb(cb[-1]))
+    return 'cb=[%s]' % cb
+
+
+def _future_repr_info(future):
+    # (Future) -> str
+    """helper function for Future.__repr__"""
+    info = [future._state.lower()]
+    if future._state == _FINISHED:
+        if future._exception is not None:
+            info.append('exception={!r}'.format(future._exception))
+        else:
+            # use reprlib to limit the length of the output, especially
+            # for very long strings
+            result = reprlib.repr(future._result)
+            info.append('result={}'.format(result))
+    if future._callbacks:
+        info.append(_format_callbacks(future._callbacks))
+    if future._source_traceback:
+        frame = future._source_traceback[-1]
+        info.append('created at %s:%s' % (frame[0], frame[1]))
+    return info