connecting to postgreSQL using psycopg2

import psycopg2 # the postgreSQL package
import sys
import optparse

host_string = "localhost"
dbname_string = "mydatabase"
username_string = "myaccount"


from optparse import OptionParser

def main():
# The entry point : obtain the password and connect database.

        parser=OptionParser()
        parser.add_option("-p", "--password", dest="password", help="password for database account", metavar="PASSWORD")
        parser.add_option("-o", "--output", dest="outfilename", help="output filename", metavar="OUTPUT_FILE")
        (options, args) = parser.parse_args()
        if len(sys.argv) < 2:
                parser.print_help()
        else:
                print ("options:", str(options))
                print ("arguments:", args)
                print options.password
                conn_string = "host="+"'"+host_string+"' "+"dbname="+"'"+ dbname_string+"' "+"user="+"'"+username_string+"' "+"password="+"'"+options.password+"'"
                print "Connecting to database\n -> %s" % (conn_string)
                try :
                        conn=psycopg2.connect(conn_string)

                except:
                        print "unable to connect to database %s on host %s for user %s" %(dbname_string) %(host_string) %s(username_string)
                print "Connected to database\n -> %s" % (conn_string)
                cur=conn.cursor() # obtain the curser to execute SQL queries
                cur.execute ("""SELECT * from system_now;""") #execute SQL query
                rows = cur.fetchall() # fetch all rows
                for row in rows: #print rows
                        print " ", row[1]
main()