import os
from cenviron import getenv, putenv       # get C module's methods

class EnvMapping:                         # wrap in a Python class
    def __setitem__(self, key, value):
        os.environ[key] = value           # on writes: Env[key]=value
        putenv(key, value)                # put in os.environ too

    def __getitem__(self, key):
        value = getenv(key)               # on reads: Env[key]
        os.environ[key] = value           # integrity check
        return value

Env = EnvMapping()                        # make one instance