class OtherType(object):  # this is the one you didn't write
  # dummy implementations for the example:
  def set(self, D):
    print "setting", D
  def status(self, key):
    return "<value of %s>" % key

class Blah(object):
  def __init__(self, parent):
    object.__setattr__(self, "_parent", parent)

  def __getattr__(self, attr):
    return self._parent.status(attr)
  def __setattr__(self, attr, value):
    self._parent.set({attr: value})

obj = Blah(OtherType())
obj.velocity = 42
print obj.velocity

setting {'velocity': 42}
<value of velocity>