python const from: http://code.activestate.com/recipes/65207-constants-in-python/?in=user-97991

const.py

# Put in const.py...:
# python2
class _const:
    class ConstError(TypeError): pass
    def __setattr__(self,name,value):
        if self.__dict__.has_key(name):
            raise self.ConstError, "Can't rebind const(%s)"%name
        self.__dict__[name]=value
import sys
sys.modules[__name__]=_const()

# that's all -- now any client-code can
import const
# and bind an attribute ONCE:
const.magic = 23
# but NOT re-bind it:
const.magic = 88      # raises const.ConstError
# you may also want to add the obvious __delattr__

const.py3

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# File              : const.py
# Author            : Svtter <svtter@qq.com>
# Date              : 06.02.2018
# Last Modified Date: 06.02.2018
# Last Modified By  : Svtter <svtter@qq.com>


class _const:
    class ConstError(TypeError):
        pass

    def __setattr__(self, name, value):
        if name in self.__dict__:
            raise self.ConstError("Can't rebind const(%s)" % name)
        self.__dict__[name] = value

import sys
sys.modules[__name__] = _const()