def get_member(self, person_id):
""" Add member if it does not exist yet, return
existing member if any.
"""
if person_id in self.members:
person = self.members[person_id]
else:
person = Person(person_id)
self.members[person_id] = person
person.get_gender()
if person.id not in ambiguous_side:
person.add_parents(self)
return person
