link.py

from pprint import pprint

foo = {'name': 'foo'}
bar = {'name': 'bar'}
baz = {'name': 'baz'}
mytopic = {'name': 'mytopic'}
myothertopic = {'name': 'myothertopic'}
can = {'name': 'can'}

foo['parent'] = mytopic
bar['parent'] = foo
baz['parent'] = mytopic
can['parent'] = myothertopic

things = [foo, myothertopic, bar, can, baz, mytopic]

tops = []
while things:
    this = things.pop()
    try:
        parent = this['parent']
    except KeyError:
        tops.append(this)
        continue
    try:
        parent['child'].append(this)
    except KeyError:
        parent['child'] = [this]

pprint(tops)

print "####### now traverse"

def traverse(node):
    try:
        children = node['child']
        print 'node ',  node['name']
        print 'kids:'
        for child in children:
            print '\t', child['name']
            traverse(child)
    except KeyError:
        return

for top in tops:
    print 'top:', top['name']
    traverse(top)