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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def commit(self):
 """Makes a ``ReadModifyWriteRow`` API request. This commits modifications made by :meth:`append_cell_value` and :meth:`increment_cell_value`. If no modifications were made, makes no API request and just returns ``{}``. Modifies a row atomically, reading the latest existing timestamp / value from the specified columns and writing a new value by appending / incrementing. The new cell created uses either the current server time or the highest timestamp of a cell in that column (if it exceeds the server time). After committing the accumulated mutations, resets the local mutations. For example: .. literalinclude:: snippets_table.py :start-after: [START bigtable_row_commit] :end-before: [END bigtable_row_commit] :rtype: dict :returns: The new contents of all modified cells. Returned as a dictionary of column families, each of which holds a dictionary of columns. Each column contains a list of cells modified. Each cell is represented with a two-tuple with the value (in bytes) and the timestamp for the cell. :raises: :class:`ValueError <exceptions.ValueError>` if the number of mutations exceeds the :data:`MAX_MUTATIONS`. """

        num_mutations = len(self._rule_pb_list)
        if num_mutations == 0:
            return {}
        if num_mutations > MAX_MUTATIONS:
            raise ValueError(
                "%d total append mutations exceed the maximum "
                "allowable %d." % (num_mutations, MAX_MUTATIONS)
            )

        data_client = self._table._instance._client.table_data_client
        row_response = data_client.read_modify_write_row(
            table_name=self._table.name, row_key=self._row_key, rules=self._rule_pb_list
        )

        # Reset modifications after commit-ing request.
        self.clear()

        # NOTE: We expect row_response.key == self._row_key but don't check.
        return _parse_rmw_row_response(row_response)