Which error constant to use for "permission deny error when updating a table that user is not allowd to "

Hello,

I am trying to catch permission denied exception. For example, user 1 is
not allowed to update table 2, when user1 updated table 2 there is a
permission excetpion.

In http://www.postgresql.org/docs/8.1/static/errcodes-appendix.html,
I tried "modifying_sql_data_not_permitted" , "sql_routine_exception",
"external_routine_exception" but none of them catch the permission deny
error.

Could someone tell me which error constant should I use to catch the
permission denied error please?

Thanks a lot!
Ying