Pair mating bears and avoid common ancestors

bears.py

import sys
import re

class Bear:
    def __init__(self, attrs):
        self.parents = []
        self.name = attrs[0]
        if len(attrs) > 1:
            self.sex = attrs[1]
            self.parents = attrs[2:4]
            self.age = float(attrs[4])

def read_file(file_):
    with open(file_) as f:
        for line in f:
            yield [b.strip() for b in line.split(':')]

def norml(name):
    return ' '.join(name.split()).upper()

def create_bears(file_):
    pnts = set()
    bears = {}
    for line in read_file(file_):
        # create bear for each line
        name = norml(line[0])
        bears[name] = Bear(line)
        # create parents if they don't exist
        pnts = pnts | set(map(norml, line[2:4]))
        for pnt in [p for p in line[2:4] if norml(p) not in bears]:
            bears[norml(pnt)] = Bear([pnt])
    # set bear parents
    set_parents(bears)
    return [b for n, b in bears.iteritems() if n not in pnts]

def set_parents(bears):
    for bear in bears.itervalues():
        bear.parents = [bears[norml(pnt)] for pnt in bear.parents if pnt]

def mate_bears(bears):
    boys, girls = find_mates(bears)
    return [(b, g) for b in boys for g in girls if can_mate(b, g)]

def find_mates(bears):
    boys = []
    girls = []
    for b in bears:
        if b.age > 2.0 and b.age < 6.0:
            if b.sex == 'M':
                boys.append(b)
            else:
                girls.append(b)
    return boys, girls

def can_mate(boy, girl):
    return not are_related(boy, girl) and abs(boy.age - girl.age) <= 1.0

def are_related(boy, girl):
    bped = pedigree(boy, [])
    gped = pedigree(girl, [])
    return len(bped & gped) > 0

def pedigree(bear, ped=[], gen=0):
    pnts = bear.parents
    if gen < 2:
        ped += pnts
    for p in pnts:
        pedigree(p, ped, gen+1)
    return set(ped)

def main(file_):
    chldn = create_bears(file_)
    mates = mate_bears(chldn)
    for boy, girl in mates:
        print ' + '.join([boy.name, girl.name])

if __name__=='__main__':
    main(sys.argv[1])