# Buggy code
def _copartition(self, axis, other, how, sort, force_repartition=False):
    """
    Copartition two dataframes.

    Perform aligning of partitions, index and partition blocks.

    Parameters
    ----------
    axis : 0 or 1
        The axis to copartition along (0 - rows, 1 - columns).
    other : BasePandasFrame
        The other dataframes(s) to copartition against.
    how : str
        How to manage joining the index object ("left", "right", etc.)
    sort : boolean
        Whether or not to sort the joined index.
    force_repartition : bool, default False
        Whether or not to force the repartitioning. By default,
        this method will skip repartitioning if it is possible. This is because
        reindexing is extremely inefficient. Because this method is used to
        `join` or `append`, it is vital that the internal indices match.

    Returns
    -------
    Tuple
        A tuple (left data, right data list, joined index).
    """
    if isinstance(other, type(self)):
        other = [other]

    # define helper functions
    def get_axis_lengths(partitions, axis):
        if axis:
            return [obj.width() for obj in partitions[0]]
        return [obj.length() for obj in partitions.T[0]]

    self_index = self.axes[axis]
    others_index = [o.axes[axis] for o in other]
    joined_index, make_reindexer = self._join_index_objects(
        axis, [self_index] + others_index, how, sort
    )

    frames = [self] + other
    non_empty_frames_idx = [i for i, o in enumerate(frames) if o._partitions.size != 0]

    # If all frames are empty
    if len(non_empty_frames_idx) == 0:
        return self._partitions, [o._partitions for o in other], joined_index

    base_frame_idx = non_empty_frames_idx[0]
    base_frame = frames[base_frame_idx]

    other_frames = frames[base_frame_idx + 1 :]

    # Picking first non-empty frame
    base_frame = frames[non_empty_frames_idx[0]]
    base_index = base_frame.axes[axis]

    # define conditions for reindexing and repartitioning `self` frame
    do_reindex_base = not base_index.equals(joined_index)
    do_repartition_base = force_repartition or do_reindex_base

    # perform repartitioning and reindexing for `base_frame` if needed
    if do_repartition_base:
        reindexed_base = base_frame._frame_mgr_cls.map_axis_partitions(
            axis,
            base_frame._partitions,
            make_reindexer(do_reindex_base, base_frame_idx),
        )
    else:
        reindexed_base = base_frame._partitions

    # define length of base and `other` frames to aligning purpose
    base_lengths = get_axis_lengths(reindexed_base, axis)
    others_lengths = [o._axes_lengths[axis] for o in other_frames]

    # define conditions for reindexing and repartitioning `other` frames
    do_reindex_others = [not o.axes[axis].equals(joined_index) for o in other_frames]

    do_repartition_others = [None] * len(other_frames)
    for i in range(len(other_frames)):
        do_repartition_others[i] = (
            force_repartition
            or do_reindex_others[i]
            or others_lengths[i] != base_lengths
        )

    # perform repartitioning and reindexing for `other` frames if needed
    reindexed_other_list = [None] * len(other_frames)
    for i in range(len(other_frames)):
        if do_repartition_others[i]:
            # indices of others frame start from `base_frame_idx` + 1
            reindexed_other_list[i] = other_frames[
                i
            ]._frame_mgr_cls.map_axis_partitions(
                axis,
                other[i]._partitions,
                make_reindexer(do_repartition_others[i], base_frame_idx + 1 + i),
                lengths=base_lengths,
            )
        else:
            reindexed_other_list[i] = other_frames[i]._partitions
    reindexed_frames = (
        [frames[i]._partitions for i in range(base_frame_idx)]
        + [reindexed_base]
        + reindexed_other_list
    )
    return reindexed_frames[0], reindexed_frames[1:], joined_index


# Traceback (Exception)
Traceback (most recent call last):
File "../rofl.py", line 10, in <module>
print(df) # Internal error
File "/localdisk/dchigare/repos/modin_bp/modin/pandas/base.py", line 2741, in __str__
return repr(self)
File "/localdisk/dchigare/repos/modin_bp/modin/pandas/dataframe.py", line 184, in __repr__
result = repr(self._build_repr_df(num_rows, num_cols))
File "/localdisk/dchigare/repos/modin_bp/modin/pandas/base.py", line 168, in _build_repr_df
return self.iloc[indexer]._query_compiler.to_pandas()
File "/localdisk/dchigare/repos/modin_bp/modin/backends/pandas/query_compiler.py", line 205, in to_pandas
return self._modin_frame.to_pandas()
File "/localdisk/dchigare/repos/modin_bp/modin/engines/base/frame/data.py", line 2098, in to_pandas
f"Internal and external indices on axis {axis} do not match.",
File "/localdisk/dchigare/repos/modin_bp/modin/error_message.py", line 63, in catch_bugs_and_request_email
" caused this error.\n{}".format(extra_log)
Exception: Internal Error. Please email bug_reports@modin.org with the traceback and command that caused this error.
Internal and external indices on axis 1 do not match.

# Fixed code
def _copartition(self, axis, other, how, sort, force_repartition=False):
    """
    Copartition two dataframes.

    Perform aligning of partitions, index and partition blocks.

    Parameters
    ----------
    axis : 0 or 1
        The axis to copartition along (0 - rows, 1 - columns).
    other : BasePandasFrame
        The other dataframes(s) to copartition against.
    how : str
        How to manage joining the index object ("left", "right", etc.)
    sort : boolean
        Whether or not to sort the joined index.
    force_repartition : bool, default False
        Whether or not to force the repartitioning. By default,
        this method will skip repartitioning if it is possible. This is because
        reindexing is extremely inefficient. Because this method is used to
        `join` or `append`, it is vital that the internal indices match.

    Returns
    -------
    Tuple
        A tuple (left data, right data list, joined index).
    """
    if isinstance(other, type(self)):
        other = [other]

    # define helper functions
    def get_axis_lengths(partitions, axis):
        if axis:
            return [obj.width() for obj in partitions[0]]
        return [obj.length() for obj in partitions.T[0]]

    self_index = self.axes[axis]
    others_index = [o.axes[axis] for o in other]
    joined_index, make_reindexer = self._join_index_objects(
        axis, [self_index] + others_index, how, sort
    )

    frames = [self] + other
    non_empty_frames_idx = [i for i, o in enumerate(frames) if o._partitions.size != 0]

    # If all frames are empty
    if len(non_empty_frames_idx) == 0:
        return self._partitions, [o._partitions for o in other], joined_index

    base_frame_idx = non_empty_frames_idx[0]
    base_frame = frames[base_frame_idx]

    other_frames = frames[base_frame_idx + 1 :]

    # Picking first non-empty frame
    base_frame = frames[non_empty_frames_idx[0]]
    base_index = base_frame.axes[axis]

    # define conditions for reindexing and repartitioning `self` frame
    do_reindex_base = not base_index.equals(joined_index)
    do_repartition_base = force_repartition or do_reindex_base

    # perform repartitioning and reindexing for `base_frame` if needed
    if do_repartition_base:
        reindexed_base = base_frame._frame_mgr_cls.map_axis_partitions(
            axis,
            base_frame._partitions,
            make_reindexer(do_reindex_base, base_frame_idx),
        )
    else:
        reindexed_base = base_frame._partitions

    # define length of base and `other` frames to aligning purpose
    base_lengths = get_axis_lengths(reindexed_base, axis)
    others_lengths = [o._axes_lengths[axis] for o in other_frames]

    # define conditions for reindexing and repartitioning `other` frames
    do_reindex_others = [not o.axes[axis].equals(joined_index) for o in other_frames]

    do_repartition_others = [None] * len(other_frames)
    for i in range(len(other_frames)):
        do_repartition_others[i] = (
            force_repartition
            or do_reindex_others[i]
            or others_lengths[i] != base_lengths
        )

    # perform repartitioning and reindexing for `other_frames` if needed
    reindexed_other_list = [None] * len(other_frames)
    for i in range(len(other_frames)):
        if do_repartition_others[i]:
            # indices of others frame start from `base_frame_idx` + 1
            reindexed_other_list[i] = other_frames[
                i
            ]._frame_mgr_cls.map_axis_partitions(
                axis,
                other_frames[i]._partitions,
                make_reindexer(do_repartition_others[i], base_frame_idx + 1 + i),
                lengths=base_lengths,
            )
        else:
            reindexed_other_list[i] = other_frames[i]._partitions
    reindexed_frames = (
        [frames[i]._partitions for i in range(base_frame_idx)]
        + [reindexed_base]
        + reindexed_other_list
    )
    return reindexed_frames[0], reindexed_frames[1:], joined_index