# Buggy code
def __getitem__(self, key):
    kwargs = self._kwargs.copy()
    # Most of time indexing DataFrameGroupBy results in another DataFrameGroupBy object unless circumstances are
    # special in which case SeriesGroupBy has to be returned. Such circumstances are when key equals to a single
    # column name and is not a list of column names or list of one column name.
    make_dataframe = True
    if self._drop:
        if not isinstance(key, list):
            key = [key]
            kwargs["squeeze"] = True
            make_dataframe = False
    # When `as_index` is False, pandas will always convert to a `DataFrame`, we
    # convert to a list here so that the result will be a `DataFrame`.
    elif not self._as_index and not isinstance(key, list):
        key = [key]
    if isinstance(key, list) and (make_dataframe or not self._as_index):
        return DataFrameGroupBy(
            self._df[key],
            self._by,
            self._axis,
            idx_name=self._idx_name,
            drop=self._drop,
            **kwargs,
        )
    return SeriesGroupBy(
        self._df[key],
        self._by,
        self._axis,
        idx_name=self._idx_name,
        drop=False,
        **kwargs,
    )


# Traceback (ray.exceptions.RayTaskError)
Traceback (most recent call last):
File "groupby_test16.py", line 29, in <module>
df1 = gb.prod()
File "/localdisk/gashiman/modin/modin/pandas/groupby.py", line 333, in prod
return self._groupby_reduce(callable, None)
File "/localdisk/gashiman/modin/modin/pandas/groupby.py", line 582, in _groupby_reduce
query_compiler=groupby_qc.groupby_reduce(
File "/localdisk/gashiman/modin/modin/backends/pandas/query_compiler.py", line 1298, in groupby_reduce
new_modin_frame = qc._modin_frame.groupby_reduce(
File "/localdisk/gashiman/modin/modin/engines/base/frame/data.py", line 1259, in groupby_reduce
new_index = self._frame_mgr_cls.get_indices(
File "/localdisk/gashiman/modin/modin/engines/ray/pandas_on_ray/frame/partition_manager.py", line 87, in get_indices
new_idx = ray.get(new_idx)
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/ray/worker.py", line 1515, in get
raise value.as_instanceof_cause()
ray.exceptions.RayTaskError(ValueError): ray::modin.engines.ray.pandas_on_ray.frame.partition.deploy_ray_func() (pid=2588931, ip=10.241.129.19)
File "python/ray/_raylet.pyx", line 427, in ray._raylet.execute_task
File "python/ray/_raylet.pyx", line 449, in ray._raylet.execute_task
ray.exceptions.RayTaskError: ray::modin.engines.ray.pandas_on_ray.frame.axis_partition.deploy_ray_func() (pid=2588931, ip=10.241.129.19)
File "python/ray/_raylet.pyx", line 427, in ray._raylet.execute_task
File "python/ray/_raylet.pyx", line 449, in ray._raylet.execute_task
ray.exceptions.RayTaskError: ray::modin.engines.ray.pandas_on_ray.frame.partition_manager.func() (pid=2588931, ip=10.241.129.19)
File "python/ray/_raylet.pyx", line 463, in ray._raylet.execute_task
File "/localdisk/gashiman/modin/modin/engines/ray/pandas_on_ray/frame/partition_manager.py", line 44, in func
return apply_func(df, other)
File "/localdisk/gashiman/modin/modin/backends/pandas/query_compiler.py", line 1248, in _map
result = map_func(
File "/localdisk/gashiman/modin/modin/pandas/groupby.py", line 332, in callable
return df.prod(**kwargs)
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/groupby.py", line 1371, in f
return self._cython_agg_general(alias, alt=npfunc, **kwargs)
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/generic.py", line 993, in _cython_agg_general
agg_blocks, agg_items = self._cython_agg_blocks(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/generic.py", line 1022, in _cython_agg_blocks
result, _ = self.grouper.aggregate(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/ops.py", line 586, in aggregate
return self._cython_operation(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/ops.py", line 529, in _cython_operation
result = self._aggregate(
File "/nfs/site/home/gashiman/.local/lib/python3.8/site-packages/pandas/core/groupby/ops.py", line 608, in _aggregate
agg_func(result, counts, values, comp_ids, min_count)
File "pandas/_libs/groupby.pyx", line 511, in pandas._libs.groupby._group_prod
File "stringsource", line 658, in View.MemoryView.memoryview_cwrapper
File "stringsource", line 349, in View.MemoryView.memoryview.__cinit__
ValueError: buffer source array is read-only

# Fixed code
def __getitem__(self, key):
    kwargs = self._kwargs.copy()
    # Most of time indexing DataFrameGroupBy results in another DataFrameGroupBy object unless circumstances are
    # special in which case SeriesGroupBy has to be returned. Such circumstances are when key equals to a single
    # column name and is not a list of column names or list of one column name.
    make_dataframe = True
    if self._drop and self._as_index:
        if not isinstance(key, list):
            key = [key]
            kwargs["squeeze"] = True
            make_dataframe = False
    # When `as_index` is False, pandas will always convert to a `DataFrame`, we
    # convert to a list here so that the result will be a `DataFrame`.
    elif not self._as_index and not isinstance(key, list):
        # Sometimes `__getitem__` doesn't only get the item, it also gets the `by`
        # column. This logic is here to ensure that we also get the `by` data so
        # that it is there for `as_index=False`.
        if (
            isinstance(self._by, type(self._query_compiler))
            and all(c in self._columns for c in self._by.columns)
            and self._drop
        ):
            key = [key] + list(self._by.columns)
        else:
            key = [key]
    if isinstance(key, list) and (make_dataframe or not self._as_index):
        return DataFrameGroupBy(
            self._df[key],
            self._by,
            self._axis,
            idx_name=self._idx_name,
            drop=self._drop,
            **kwargs,
        )
    return SeriesGroupBy(
        self._df[key],
        self._by,
        self._axis,
        idx_name=self._idx_name,
        drop=False,
        **kwargs,
    )