Trying to solve the problem of using context managers with transaction pools

db_context_mgr.py

from contextlib import contextmanager
from contextlib import ContextDecorator
import psycopg2
from sqlalchemy import create_engine
import os
import uuid


class DBTask(object):
    def __init__(self, name='anonymous DB task'):
        self.name = name
        self._id = None
    
    def _get_uuid(self):
        # can be overridden in descendant classes
        return uuid.uuid4()
    
    def __str__(self):
        return 'dbtask[%s]:%s' % (self.name, self.uuid)
    
    @property
    def uuid(self):
        if not self._id:
            self._id = self._get_uuid()
        return self._id
        

class ConnectionPoolManager(Object):
    def __init__(self, hostname, db_name, username, password, port='5432'):
        #self.connect_string = 'postgresql://'+user+':'+password+'@'+host+':'+port+'/'+dbname
        #conn = create_engine(connect_string, pool_size=20, max_overflow_size=0)
        self.hostname = hostname
        self.dbname = db_name
        self.username = username
        self.password = password
        self.port = port
        self.connection_pool = pool.QueuePool(self._getconn,
                                             max_overflow=10,
                                             pool_size=5)
        self.connection_table = {}
        
        
        
    def _get_connection(self): # can override in subclasses
        c = psycopg2.connect(username=self.username,
                            host=self.hostname,
                            dbname=self.dbname,
                            password=self.password,
                            port=self.port)
        return c

    
    def get_connection(self, db_task):
        conn = self._get_connection()
        self.connection_table[db_task.uuid()] = conn
        return conn
    

@contextmanager
def get_connection(connection_pool_mgr, db_task):    
    conn = connection_mgr.get_connection(db_task)
    yield conn
    connection_mgr.close_connection(db_task)
    
    
cpmgr = ConnectionPoolManager('mydb', ...)
with get_connection(cpmgr, DBTask('update table')) as conn:
    ...
    ...