def _combine_transfers(self, result):
transfers = {}<EOL>for reaction_id, c1, c2, form in result:<EOL><INDENT>key = reaction_id, c1, c2<EOL>combined_form = transfers.setdefault(key, Formula())<EOL>transfers[key] = combined_form | form<EOL><DEDENT>for (reaction_id, c1, c2), form in iteritems(transfers):<EOL><INDENT>yield reaction_id, c1, c2, form<EOL><DEDENT>
Combine multiple pair transfers into one.