diff --git a/README.md b/README.md
index dd01447..4cc2a46 100755
--- a/README.md
+++ b/README.md
@@ -28,7 +28,7 @@ SQLOR is a database api for python3, it is base on the python's DBAPI2
 ```
 import asyncio
 
-from sqlor.dbpools  import DBPools
+from sqlor.dbpools  import DBPools, sqlorContext
 
 dbs={
         "aiocfae":{
@@ -72,8 +72,7 @@ loop = asyncio.get_event_loop()
 pool = DBPools(dbs,loop=loop)
 
 async def testfunc():
-        db = DBPools()
-		async with db.sqlorContext('stock') as sor:	
+		async with sqlorContext('stock') as sor:	
 			# start a transaction
 			# if exception happended, all change to database will rollback
 			# else will commit
diff --git a/sqlor/sor.py b/sqlor/sor.py
index 5371c76..8c8743e 100755
--- a/sqlor/sor.py
+++ b/sqlor/sor.py
@@ -80,7 +80,7 @@ class SQLor(object):
 		self.sqlts = sqlts
 		self.sqlvp = sqlvp
 		self.sqlvs = sqlvs
-		self.dbdesc = dbdesc
+		self.dbdesc = dbdesc.copy()
 		self.unpassword()
 		self.dbname = None
 		self.writer = None