# Buggy code
def put(self, session_id, data_key, value):
    """
    Put a Mars object into plasma store
    :param session_id: session id
    :param data_key: chunk key
    :param value: Mars object to be put
    """
    data_size = None

    try:
        obj_id = self._new_object_id(session_id, data_key)
    except StorageDataExists:
        obj_id = self._get_object_id(session_id, data_key)
        if self._plasma_client.contains(obj_id):
            logger.debug("Data %s already exists, returning existing", data_key)
            [buffer] = self._plasma_client.get_buffers([obj_id], timeout_ms=10)
            del value
            return buffer
        else:
            logger.warning(
                "Data %s registered but no data found, reconstructed", data_key
            )
            self._mapper_ref.delete(session_id, data_key)
            obj_id = self._new_object_id(session_id, data_key)

    try:
        try:
            serialized = dataserializer.serialize(value)
        except SerializationCallbackError:
            self._mapper_ref.delete(session_id, data_key)
            raise SerializationFailed(obj=value) from None

        del value
        data_size = serialized.total_bytes
        try:
            buffer = self._plasma_client.create(obj_id, serialized.total_bytes)
            stream = pyarrow.FixedSizeBufferWriter(buffer)
            stream.set_memcopy_threads(6)
            self._pool.submit(serialized.write_to, stream).result()
            self._plasma_client.seal(obj_id)
        finally:
            del serialized
        return buffer
    except PlasmaStoreFull:
        self._mapper_ref.delete(session_id, data_key)
        logger.warning(
            "Data %s(%d) failed to store to plasma due to StorageFull",
            data_key,
            data_size,
        )
        exc = PlasmaStoreFull
    except:  # noqa: E722
        self._mapper_ref.delete(session_id, data_key)
        raise

    if exc is PlasmaStoreFull:
        raise StorageFull(
            request_size=data_size, capacity=self._size_limit, affected_keys=[data_key]
        )


# Traceback (AttributeError)
AttributeError                            Traceback (most recent call last)
<ipython-input-3-a85925f048d0> in <module>
1 start=time.time()
2 df_mars=df_mars.to_gpu()
----> 3 print(df_mars.sum().to_frame(name="sum").execute())

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/core.py in execute(self, session, **kw)
580
581     def execute(self, session=None, **kw):
--> 582         self._data.execute(session, **kw)
583         return self
584

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/core.py in execute(self, session, **kw)
368
369         # no more fetch, thus just fire run
--> 370         session.run(self, **kw)
371         # return Tileable or ExecutableTuple itself
372         return self

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/session.py in run(self, *tileables, **kw)
460         tileables = tuple(mt.tensor(t) if not isinstance(t, (Entity, Base)) else t
461                           for t in tileables)
--> 462         result = self._sess.run(*tileables, **kw)
463
464         for t in tileables:

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/session.py in run(self, *tileables, **kw)
105             # set number of running cores
106             self.context.set_ncores(kw['n_parallel'])
--> 107             res = self._executor.execute_tileables(tileables, **kw)
108             return res
109

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/utils.py in _wrapped(*args, **kwargs)
406                 _kernel_mode.eager = False
407             _kernel_mode.eager_count = enter_eager_count + 1
--> 408             return func(*args, **kwargs)
409         finally:
410             _kernel_mode.eager_count -= 1

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/utils.py in inner(*args, **kwargs)
500     def inner(*args, **kwargs):
501         with build_mode():
--> 502             return func(*args, **kwargs)
503     return inner
504

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in execute_tileables(self, tileables, fetch, n_parallel, n_thread, print_progress, mock, compose, name)
878                                    n_parallel=n_parallel or n_thread,
879                                    print_progress=print_progress, mock=mock,
--> 880                                    chunk_result=chunk_result)
881
882                 # update shape of tileable and its chunks whatever it's successful or not

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in execute_graph(self, graph, keys, n_parallel, print_progress, mock, no_intermediate, compose, retval, chunk_result)
688             print_progress=print_progress, mock=mock, mock_max_memory=self._mock_max_memory,
689             fetch_keys=fetch_keys, no_intermediate=no_intermediate)
--> 690         res = graph_execution.execute(retval)
691         self._mock_max_memory = max(self._mock_max_memory, graph_execution._mock_max_memory)
692         if mock:

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in execute(self, retval)
569         # wait until all the futures completed
570         for future in executed_futures:
--> 571             future.result()
572
573         if retval:

/opt/conda/envs/rapids/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
423                 raise CancelledError()
424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
426
427             self._condition.wait(timeout)

/opt/conda/envs/rapids/lib/python3.6/concurrent/futures/_base.py in __get_result(self)
382     def __get_result(self):
383         if self._exception:
--> 384             raise self._exception
385         else:
386             return self._result

/opt/conda/envs/rapids/lib/python3.6/concurrent/futures/thread.py in run(self)
54
55         try:
---> 56             result = self.fn(*self.args, **self.kwargs)
57         except BaseException as exc:
58             self.future.set_exception(exc)

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in _execute_operand(self, op)
441             # so we pass the first operand's first output to Executor.handle
442             first_op = ops[0]
--> 443             Executor.handle(first_op, results, self._mock)
444
445             # update maximal memory usage during execution

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in handle(cls, op, results, mock)
639                 # The `UFuncTypeError` was introduced by numpy#12593 since v1.17.0.
640                 try:
--> 641                     return runner(results, op)
642                 except UFuncTypeError as e:
643                     raise TypeError(str(e)).with_traceback(sys.exc_info()[2]) from None

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/dataframe/reduction/core.py in execute(cls, ctx, op)
405                 cls._execute_agg(ctx, op)
406             elif op.stage == OperandStage.map:
--> 407                 cls._execute_map(ctx, op)
408             else:
409                 in_data = ctx[op.inputs[0].key]

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/dataframe/reduction/core.py in _execute_map(cls, ctx, op)
380             cls._execute_map_with_count(ctx, op)
381         else:
--> 382             cls._execute_without_count(ctx, op)
383
384     @classmethod

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/dataframe/reduction/core.py in _execute_without_count(cls, ctx, op, reduction_func)
370                 # cannot just do xdf.DataFrame(r).T
371                 # cuz the dtype will be object since pandas 1.0
--> 372                 df = xdf.DataFrame(OrderedDict((d, [v]) for d, v in r.iteritems()))
373             else:
374                 df = xdf.DataFrame(r)

AttributeError: 'Series' object has no attribute 'iteritems'

# Fixed code
def put(self, session_id, data_key, value):
    """
    Put a Mars object into plasma store
    :param session_id: session id
    :param data_key: chunk key
    :param value: Mars object to be put
    """
    data_size = None

    try:
        obj_id = self._new_object_id(session_id, data_key)
    except StorageDataExists:
        obj_id = self._get_object_id(session_id, data_key)
        if self._plasma_client.contains(obj_id):
            logger.debug("Data %s already exists, returning existing", data_key)
            [buffer] = self._plasma_client.get_buffers([obj_id], timeout_ms=10)
            del value
            return buffer
        else:
            logger.warning(
                "Data %s registered but no data found, reconstructed", data_key
            )
            self._mapper_ref.delete(session_id, data_key)
            obj_id = self._new_object_id(session_id, data_key)

    try:
        try:
            serialized = dataserializer.serialize(value)
        except SerializationCallbackError:
            self._mapper_ref.delete(session_id, data_key)
            raise SerializationFailed(obj=value) from None

        del value
        data_size = serialized.total_bytes
        try:
            buffer = self._plasma_client.create(obj_id, serialized.total_bytes)
            stream = pyarrow.FixedSizeBufferWriter(buffer)
            stream.set_memcopy_threads(6)
            self._pool.submit(serialized.write_to, stream).result()
            self._plasma_client.seal(obj_id)
        finally:
            del serialized
        return buffer
    except plasma_errors.PlasmaStoreFull:
        self._mapper_ref.delete(session_id, data_key)
        logger.warning(
            "Data %s(%d) failed to store to plasma due to StorageFull",
            data_key,
            data_size,
        )
        exc = plasma_errors.PlasmaStoreFull
    except:  # noqa: E722
        self._mapper_ref.delete(session_id, data_key)
        raise

    if exc is plasma_errors.PlasmaStoreFull:
        raise StorageFull(
            request_size=data_size, capacity=self._size_limit, affected_keys=[data_key]
        )