I want update one record using ADO,but I can't ,why?

[nightmarch]

I want update one record ,but I can't ,why?

code like following:

##-------------------------------------------------
import win32com.client as wc
    
def main():
    conn = wc.Dispatch(r'ADODB.Connection')
    rs = wc.Dispatch(r'ADODB.Recordset')    
    connStr = "Provider=MSDAORA.1;Password=jmpower;User
ID=jmpower;Data Source=jmgis_agps3;Persist Security Info=True"
    tblName = r'wjtmp'

    conn.Open(connStr )

    rs.Open( tblName, conn, wc.constants.adOpenKeyset,
wc.constants.adLockOptimistic )
    
    if rs.Supports( wc.constants.adUpdate ):
        rs.Fields.Item(0).Value = 11
        rs.Update()    
    else:
        print "recordset can't update"
        
    rs.Close()
    conn.Close()

if __name__ == '__main__':
    main()
##-------------------------------------------------


thanks!