>>> class MyClass(namedtuple('_MyClass', ['x', 'y', 'z'])):
  ...   def foo(self):
  ...     return self.x * self.y + self.z
  ... 
  >>> x = MyClass(4, 5, 6)
  >>> x.foo()
  26

  >>> import attr
  >>> @attr.s(frozen=True)
  ... class MyClass:
  ...   x = attr.ib()
  ...   y = attr.ib()
  ...   z = attr.ib()
  ...   def foo(self):
  ...     return self.x * self.y + self.z
  ... 
  >>> x = MyClass(4, 5, 6)
  >>> x.foo()
  26