def read_row(self, row_key, filter_=None, timeout_seconds=None):
"""Read a single row from this table.
:type row_key: bytes
:param row_key: The key of the row to read from.
:type filter_: :class:`.row.RowFilter`, :class:`.row.RowFilterChain`,
:class:`.row.RowFilterUnion` or
:class:`.row.ConditionalRowFilter`
:param filter_: (Optional) The filter to apply to the contents of the
row. If unset, returns the entire row.
:type timeout_seconds: int
:param timeout_seconds: Number of seconds for request time-out.
If not passed, defaults to value set on table.
:rtype: :class:`.PartialRowData`, :data:`NoneType <types.NoneType>`
:returns: The contents of the row if any chunks were returned in
the response, otherwise :data:`None`.
:raises: :class:`ValueError <exceptions.ValueError>` if a commit row
chunk is never encountered.
"""
request_pb = _create_row_request(self.name, row_key=row_key,
filter_=filter_)
timeout_seconds = timeout_seconds or self.timeout_seconds
response_iterator = self.client.data_stub.ReadRows(request_pb,
timeout_seconds)
# We expect an iterator of `data_messages_pb2.ReadRowsResponse`
result = PartialRowData(row_key)
for read_rows_response in response_iterator:
result.update_from_read_rows(read_rows_response)
# Make sure the result actually contains data.
if not result._chunks_encountered:
return None
# Make sure the result was committed by the back-end.
if not result.committed:
raise ValueError('The row remains partial / is not committed.')
return result
