python use sqlachemy thread pool

from django.db import transaction, load_backend
from testdjango import settings
from sqlalchemy import pool
pool_initialized = False

class hashabledict(dict):
    def __hash__(self):
        return hash(tuple(sorted(self.items())))

class hashablelist(list):
    def __hash__(self):
        return hash(tuple(sorted(self)))

class ManagerProxy(object):
    def __init__(self, manager):
        self.manager = manager

    def __getattr__(self, key):
        return getattr(self.manager, key)

    def connect(self, *args, **kwargs):
        if 'conv' in kwargs:
            conv = kwargs['conv']
            if isinstance(conv, dict):
                items = []
                for k, v in conv.items():
                    if isinstance(v, list):
                        v = hashablelist(v)
                    items.append((k, v))
                kwargs['conv'] = hashabledict(items)
        return self.manager.connect(*args, **kwargs)

POOL_SETTINGS = {'max_overflow': 10, 'pool_size': 5}

def init_pool():
    if not globals().get('pool_initialized', False):
        global pool_initialized
        pool_initialized = True
        try:
            backendname = settings.DATABASES['default']['ENGINE']
            backend = load_backend(backendname)
            backend.Database = ManagerProxy(pool.manage(backend.Database, **POOL_SETTINGS))
            # backend.Database = pool.manage(backend.Database)
            backend.DatabaseError = backend.Database.DatabaseError
            backend.IntegrityError = backend.Database.IntegrityError
            logging.info("Connection Pool initialized")
        except:
            logging.exception("Connection Pool initialization error")
init_pool()