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#!/usr/bin/env python

# -*- encoding: utf-8 -*-

"""

Constant types in Python.

"""

__doc__ = """

This is a variation on "Constants in Python" by Alex Martelli, from which the

solution idea was borrowed, and enhanced according suggestions of Zoran Isailovski.

In Python, any variable can be re-bound at will -- and modules don't let you

define special methods such as an instance's __setattr__ to stop attribute

re-binding. Easy solution (in Python 2.1 and up): use an instance as "module"...

In Python 2.1 and up, no check is made any more to force entries in sys.modules

to be actually module objects. You can install an instance object there and take

advantage of its attribute-access special methods (e.g., as in this snippet, to

prevent type rebindings.

Usage:

import consttype

consttype.magic = 23 # Bind an attribute to a type ONCE

consttype.magic = 88 # Re-bind it to a same type again

consttype.magic = "one" # But NOT re-bind it to another type: this raises consttype._ConstError

del consttype.magic # Remove an named attribute

consttype.__del__() # Remove all attributes

"""

class _consttype:

class _ConstTypeError(TypeError):

pass

def __repr__(self):

return "Constant type definitions."

def __setattr__(self, name, value):

v = self.__dict__.get(name, value)

if type(v) is not type(value):

raise self._ConstTypeError("Can't rebind %s to %s" % (type(v), type(value)))

self.__dict__[name] = value

def __del__(self):

self.__dict__.clear()

import sys

sys.modules[__name__] = _consttype()

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