gncxml - join transfer account information if a transaction consists of only two splits

join_transfer.py

import gncxml

def join_transfer(sp):
    pairs = sp.reset_index() \
                .groupby(["trn_idtype", "trn_id"]) \
                .filter(lambda x: len(x) == 2)
    dup = pairs[["trn_idtype", "trn_id", "idtype", "id"]] \
              .join(pairs.set_index(["trn_idtype", "trn_id"]) \
                        .add_prefix("transfer_"), \
                    on=["trn_idtype", "trn_id"])
    dedup = dup[(dup["id"] != dup["transfer_id"]) \
                | (dup["idtype"] != dup["transfer_idtype"])] \
                .drop(columns=["trn_idtype", "trn_id"])
    return sp.join(dedup.set_index(["idtype", "id"]))

try:
    book = gncxml.Book("mybook.gnucash")
except OSError as err:
    sys.exit(err)

join_transfer(book.list_splits())