gistfile1.py

p = lambda fun: lambda arg: (lambda m: fun(arg(m))) if callable(arg) \
                                else fun(arg)

agent = p(lambda m: m.agent)
parent = p(lambda m: m.parent)

class D: pass
m1 = D()
m1.agent = 'agentm1'

m2 = D()
m2.agent = 'agentm2'
m2.parent = m1

m3 = D()
m3.parent = m2

selector = agent(parent(parent))

print selector(m3)