Example for merging item records spread out over multiple MARCXML into a single record.

item_joiner.py

#!/usr/bin/env python

# Merges items spread over multiple MARC XML records
# into a single record.  Some ILSes will not export MARC21
# that is "too large", and will output the same bibliographic record
# multiple times.

# usage: first, convert your marc21 to MARCXML (see marcrenaissance.sh gist)
# ensure that all records with the same control number come out in a 'clump',
# e.g. by sorting on control number

# reads from STDIN and outputs to STDOUT, so, e.g.
# ./item_joiner.py < multirecord.xml > joined.xml

# reads from 'multirecord.xml' and outputs to `joined.xml`.

# Check the id_expr and item_expr to make sure they're appropriate to your
# records

from lxml import etree
import sys

nsuri = "http://www.loc.gov/MARC21/slim"

mns = {'marc': nsuri}
nonens = {None: nsuri}

# NCSU keeps local control number in the 918$a; adjust as appropriate
id_expr = "marc:datafield[@tag='918']/marc:subfield[@code='a']"

# As above, you may need to adjust if you use the 949, e.g.
item_expr = "marc:datafield[@tag='999']"


def serialize(rec):
    return etree.tostring(rec, encoding="utf-8")


def extract_id(rec):
    return rec.xpath(id_expr, namespaces=mns)[0].text


def merge_items(to_rec, from_rec):
    items = from_rec.xpath(item_expr, namespaces=nonens)
    for i in items:
        to_rec.append(i)
    if items is None:
        raise ValueError(etree.tostring(from_rec))


def main(infile, outfile):
    current_id = None
    current_rec = None
    with etree.xmlfile(outfile, encoding="utf-8", buffered=True) as xf:
        with xf.element("{%s}collection" % nsuri, nsmap=nonens) as ew:
            for evt, rec in etree.iterparse(sys.stdin, events=('end',), tag='{%s}record' % nsuri):
                this_id = extract_id(rec)
            if this_id is None:
                raise ValueError("missing catkey on record")
            if this_id != current_id:
                if current_rec is not None:
                    ew.write(current_rec)
                current_rec = rec
                urrent_id = this_id
            else:
                merge_items(current_rec, rec)
            xf.write(current_rec)


if __name__ == '__main__':
    main(sys.stdin, sys.stdout)