const example

const.py

# const decorator
def const(f):
    def fset(self, value):
        raise TypeError
    def fget(self):
        return f(self)
    return property(fget, fset)

# example with class
class Data(object):
  def __init__(self, x):
    self._x_init = x

  @const
  def x(self):
    return self._x_init

# will produce error
x = 5
d = Data(x)
d.x = 6