PL/Python error fetching next item from iterator

CREATE TYPE dmkh_return AS

   (ma_kh character varying,

    ten_kh character varying,

    ten_kh2 character varying,

    dia_chi character varying,

    ma_so_thue character varying,

    loai_kh smallint,

    nh_kh1 character varying,

    nh_kh2 character varying,

    nh_kh3 character varying,

    status character varying);

ALTER TYPE dmkh_return OWNER TO postgres;

CREATE OR REPLACE FUNCTION list_khachhang()

  RETURNS SETOF dmkh_return AS

$BODY$

import pyodbc

cnxn = pyodbc.connect('DRIVER={SQL Server};SERVER=127.0.0.1,2205;DATABASE=TEST;UID=itg;PWD=')

dbcursor = cnxn.cursor()

dbcursor.execute("select ma_kh, dbo.ff_v2u(ten_kh) as ten_kh, '' as ten_kh2, '' as dia_chi, '' as ma_so_thue, CASE WHEN loai_kh IS NULL THEN 0 ELSE loai_kh END as loai_kh, nh_kh1, nh_kh2, nh_kh3, '1' as status from dmkh")

rows = dbcursor.fetchall()

for row in _rows:

yield row

$BODY$

  LANGUAGE plpythonu VOLATILE

  COST 100

  ROWS 1000;

ALTER FUNCTION list_khachhang() OWNER TO postgres;

CREATE TYPE dmdv_return AS

   (ma_dv character varying,

    ten_dv character varying,

    ten_dv2 character varying,

    nh_dv1 character varying,

    nh_dv2 character varying,

    nh_dv3 character varying,

    status character varying);

ALTER TYPE dmdv_return OWNER TO postgres;

CREATE OR REPLACE FUNCTION list_dichvu()

  RETURNS SETOF dmdv_return AS

$BODY$

import pyodbc

cnxn = pyodbc.connect('DRIVER={SQL Server};SERVER=127.0.0.1,2205;DATABASE=TEST;UID=itg;PWD=')

dbcursor = cnxn.cursor()

dbcursor.execute("select ma_dv, dbo.ff_v2u(ten_dv) as ten_dv, dbo.ff_v2u(ten_dv2) as ten_dv2, nh_dv1, nh_dv2, nh_dv3, '1' as status from dmdv")

rows = dbcursor.fetchall()

for row in rows:

yield row

$BODY$

  LANGUAGE plpythonu VOLATILE

  COST 100

  ROWS 1000;

ALTER FUNCTION list_dichvu() OWNER TO postgres;

ERROR:  error fetching next item from iterator

CONTEXT:  PL/Python function "list_khachhang"

********** Error **********

ERROR: error fetching next item from iterator

SQL state: 22000

Context: PL/Python function "list_khachhang"