cl.py

class Observable(object):
  def __init__(self, **kwargs):
    for key, val in kwargs.items():
      setattr(self, key, val)

  def __format(self):
    attrs = ['%s=%s' % (key, val)
             for key, val in self.__dict__.iteritems() if not key.startswith('_')]
    return 'Observable(%s)' % (', '.join(attrs))

  def __str__(self):
    return self.__format()

  def __repl__(self):
    return self.__format()

class X(Observable):
  pass

if __name__ == '__main__':
  o = X(foo=1, bar=5, _bazz=12,
        name='Amok', props=('One', 'two'))

  print(o)
  print(o.foo)