def crosslisting_feature(catalog, soup):
"""Parses all the crosslistings. These refer to the similar CRNs,
such as a grad & undergrad level course.
"""
listing = {}
for elem in soup.coursedb.findAll('crosslisting'):
seats = int(elem['seats'])
crns = [safeInt(crn.string) for crn in elem.findAll('crn')]
# we want to refer to the same object to save space
cl = CrossListing(crns, seats)
for crn in crns:
listing[crn] = cl
catalog.crosslistings = FrozenDict(listing)
logger.info('Catalog has %d course crosslistings' % len(catalog.crosslistings))