'Converts a batch of RDFValues at once.
This is a default non-optimized dumb implementation. Subclasses are
supposed to have their own optimized implementations.
Metadata object is provided by the caller. It contains basic information
about where the value is coming from (i.e. client_urn, session_id, etc)
as well as timestamps corresponding to when data was generated and
exported.
ExportConverter should use the metadata when constructing export-friendly
RDFValues.
Args:
metadata_value_pairs: a list or a generator of tuples (metadata, value),
where metadata is ExportedMetadata to be used for
conversion and value is an RDFValue to be converted.
token: Security token.
Yields:
Resulting RDFValues. Empty list is a valid result and means that
conversion wasn\'t possible. Resulting RDFValues may be of different
types.'

def BatchConvert(self, metadata_value_pairs, token=None):

    for (metadata, value) in metadata_value_pairs:
        for result in self.Convert(metadata, value, token):
            (yield result)
