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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 row(self, row_key, filter_=None, append=False):
 """Factory to create a row associated with this table. For example: .. literalinclude:: snippets_table.py :start-after: [START bigtable_table_row] :end-before: [END bigtable_table_row] .. warning:: At most one of ``filter_`` and ``append`` can be used in a :class:`~google.cloud.bigtable.row.Row`. :type row_key: bytes :param row_key: The key for the row being created. :type filter_: :class:`.RowFilter` :param filter_: (Optional) Filter to be used for conditional mutations. See :class:`.ConditionalRow` for more details. :type append: bool :param append: (Optional) Flag to determine if the row should be used for append mutations. :rtype: :class:`~google.cloud.bigtable.row.Row` :returns: A row owned by this table. :raises: :class:`ValueError <exceptions.ValueError>` if both ``filter_`` and ``append`` are used. """

        if append and filter_ is not None:
            raise ValueError("At most one of filter_ and append can be set")
        if append:
            return AppendRow(row_key, self)
        elif filter_ is not None:
            return ConditionalRow(row_key, self, filter_=filter_)
        else:
            return DirectRow(row_key, self)