Your definitions do not work.

  foo = (1,2,3)
  bar = (4,5,6)

  print cons(foo, bar)
  print car(foo)

console output:

  <function <lambda> at 0x00B3F430>
  Traceback (most recent call last):
    File "./test.py", line 14, in <module>
      print car(foo)
    File "./test.py", line 5, in car
      return p(lambda a,b: a)
  TypeError: 'tuple' object is not callable