IMap._cache(cpath, arg) is an internally-called method that saves the dict of arguments to
          cache files in the given cpath directory.

def _cache(cpath, arg):
        '''
        IMap._cache(cpath, arg) is an internally-called method that saves the dict of arguments to
          cache files in the given cpath directory.
        '''
        if not os.path.isdir(cpath): os.makedirs(cpath)
        for (k,v) in six.iteritems(arg):
            save(os.path.join(cpath, k + '.pp'), v, create_directories=True, overwrite=True)
        return True