singlenton.py

from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker

class ConnectPSQL(object):
    _instance = None
    _session = None
    def __new__(cls, *args, **kwargs):
        if not cls._instance:
            cls._instance = super(ConnectPSQL, cls).__new__(cls, *args, **kwargs)
            Session = None
            try:
                #engine = create_engine(options['postgres'], client_encoding='utf8', echo=True)
                engine = create_engine('postgresql+psycopg2://dondeviene:pass@localhost/dondeviene')
                Session = scoped_session(sessionmaker(autocommit=False,autoflush=False,bind=engine))
                cls._session = Session
            except:
                print "Error Connect to database"
                exit()
        return cls._instance

    def get_session(self):
        print self._session


class SingletonMetaClass(type):
    def __init__(cls,name,bases,dict):
        super(SingletonMetaClass,cls)\
          .__init__(name,bases,dict)
        original_new = cls.__new__
        def my_new(cls,*args,**kwds):
            if cls.instance == None:
                cls.instance = \
                  original_new(cls,*args,**kwds)
            return cls.instance
        cls.instance = None
        cls.__new__ = staticmethod(my_new)