ContextLocal.py

class ContextLocal(object):
    __slots__ = ('_local_init_args', '_local_contexts', '_local_context_ident')
    def __new__(cls, *args, **kwargs):
        self = object.__new__(cls)
        object.__setattr__(self, '_local_init_args', (args, kwargs))
        object.__setattr__(self, '_local_contexts', {})
        object.__setattr__(self, '_local_context_ident', lambda: 0)
        return self        
    def set_context_ident(self, func):
        object.__setattr__(self, '_local_context_ident', func)
    def _get_local(self):
        cur = self._local_context_ident()
        context = self._local_contexts.get(cur)
        if not context:
            self._local_contexts[cur] = context = {}
            args, kwargs = self._local_init_args
            self.__init__(*args, **kwargs)
        return context
    def __getattr__(self, attr):
        try:
            return self._get_local()[attr]
        except KeyError:
            raise AttributeError(attr)
    def __setattr__(self, attr, value):
        self._get_local()[attr] = value
    def __delattr__(self, attr):
        try:
            del self._get_local()[attr]
        except KeyError:
            raise AttributeError(attr)

# threading.local example

import thread
class ThreadLocal(ContextLocal):
    def _local_context_ident(self):
        thread.getCurrentThread()