groups.py

class Item(object):
    def __init__(self, name):
        self.name = name
        self.links = []

    def __repr__(self):
        return self.name


a, b, c, d, e, f, g, h = (Item(x) for x in 'abcdefgh')
a.links = [c]
b.links = [e, d]
d.links = [h]
g.links = [a]

mylist = [a, b, c, d, e, f, g, h]
groups = [[x] for x in mylist]

for item in mylist:
    for other in item.links:
        igrp, ogrp = (next(y for y in groups if x in y) for x in (item, other))
        for grp in igrp, ogrp:
            try:
                groups.remove(grp)
            except ValueError:
                pass
        groups.append(igrp + ogrp)

print groups # [[f], [b, e, d, h], [g, a, c]]