RustPython
diff --git a/‎Lib/concurrent/futures/_base.py
+36-38 b/‎Lib/concurrent/futures/_base.py
+36-38
@@ -284,13 +284,14 @@ def wait(fs, timeout=None, return_when=ALL_COMPLETED):
         A named 2-tuple of sets. The first set, named 'done', contains the
         futures that completed (is finished or cancelled) before the wait
         completed. The second set, named 'not_done', contains uncompleted
-        futures.
+        futures. Duplicate futures given to *fs* are removed and will be 
+        returned only once.
     """
+    fs = set(fs)
     with _AcquireFutures(fs):
-        done = set(f for f in fs
-                   if f._state in [CANCELLED_AND_NOTIFIED, FINISHED])
-        not_done = set(fs) - done
-
+        done = {f for f in fs
+                   if f._state in [CANCELLED_AND_NOTIFIED, FINISHED]}
+        not_done = fs - done
         if (return_when == FIRST_COMPLETED) and done:
             return DoneAndNotDoneFutures(done, not_done)
         elif (return_when == FIRST_EXCEPTION) and done:
@@ -309,7 +310,7 @@ def wait(fs, timeout=None, return_when=ALL_COMPLETED):
             f._waiters.remove(waiter)
 
     done.update(waiter.finished_futures)
-    return DoneAndNotDoneFutures(done, set(fs) - done)
+    return DoneAndNotDoneFutures(done, fs - done)
 
 class Future(object):
     """Represents the result of an asynchronous computation."""
@@ -380,13 +381,17 @@ def running(self):
             return self._state == RUNNING
 
     def done(self):
-        """Return True of the future was cancelled or finished executing."""
+        """Return True if the future was cancelled or finished executing."""
         with self._condition:
             return self._state in [CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED]
 
     def __get_result(self):
         if self._exception:
-            raise self._exception
+            try:
+                raise self._exception
+            finally:
+                # Break a reference cycle with the exception in self._exception
+                self = None
         else:
             return self._result
 
@@ -426,20 +431,24 @@ def result(self, timeout=None):
                 timeout.
             Exception: If the call raised then that exception will be raised.
         """
-        with self._condition:
-            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
-                raise CancelledError()
-            elif self._state == FINISHED:
-                return self.__get_result()
-
-            self._condition.wait(timeout)
-
-            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
-                raise CancelledError()
-            elif self._state == FINISHED:
-                return self.__get_result()
-            else:
-                raise TimeoutError()
+        try:
+            with self._condition:
+                if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                    raise CancelledError()
+                elif self._state == FINISHED:
+                    return self.__get_result()
+
+                self._condition.wait(timeout)
+
+                if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                    raise CancelledError()
+                elif self._state == FINISHED:
+                    return self.__get_result()
+                else:
+                    raise TimeoutError()
+        finally:
+            # Break a reference cycle with the exception in self._exception
+            self = None
 
     def exception(self, timeout=None):
         """Return the exception raised by the call that the future represents.
@@ -550,7 +559,7 @@ def set_exception(self, exception):
 class Executor(object):
     """This is an abstract base class for concrete asynchronous executors."""
 
-    def submit(*args, **kwargs):
+    def submit(self, fn, /, *args, **kwargs):
         """Submits a callable to be executed with the given arguments.
 
         Schedules the callable to be executed as fn(*args, **kwargs) and returns
@@ -559,21 +568,7 @@ def submit(*args, **kwargs):
         Returns:
             A Future representing the given call.
         """
-        if len(args) >= 2:
-            pass
-        elif not args:
-            raise TypeError("descriptor 'submit' of 'Executor' object "
-                            "needs an argument")
-        elif 'fn' in kwargs:
-            import warnings
-            warnings.warn("Passing 'fn' as keyword argument is deprecated",
-                          DeprecationWarning, stacklevel=2)
-        else:
-            raise TypeError('submit expected at least 1 positional argument, '
-                            'got %d' % (len(args)-1))
-
         raise NotImplementedError()
-    submit.__text_signature__ = '($self, fn, /, *args, **kwargs)'
 
     def map(self, fn, *iterables, timeout=None, chunksize=1):
         """Returns an iterator equivalent to map(fn, iter).
@@ -619,7 +614,7 @@ def result_iterator():
                     future.cancel()
         return result_iterator()
 
-    def shutdown(self, wait=True):
+    def shutdown(self, wait=True, *, cancel_futures=False):
         """Clean-up the resources associated with the Executor.
 
         It is safe to call this method several times. Otherwise, no other
@@ -629,6 +624,9 @@ def shutdown(self, wait=True):
             wait: If True then shutdown will not return until all running
                 futures have finished executing and the resources used by the
                 executor have been reclaimed.
+            cancel_futures: If True then shutdown will cancel all pending
+                futures. Futures that are completed or running will not be
+                cancelled.
         """
         pass