select
    nspname                      as schemaname
  , array_to_string(nspacl, ',') as acls
from
    pg_namespace
where
    nspacl is not null
and nspowner != 1
and array_to_string(nspacl, ',') like '%u_A=%' -- REPLACE USERNAME
;

select
    pg_namespace.nspname as schemaname
  , pg_class.relname as tablename
  , array_to_string(pg_class.relacl, ',') as acls
from pg_class
left join pg_namespace on pg_class.relnamespace = pg_namespace.oid
where
    pg_class.relacl is not null
and pg_namespace.nspname not in (
    'pg_catalog'
  , 'pg_toast'
  , 'information_schema'
)
and array_to_string(pg_class.relacl, ',') like '%u_A=%' -- REPLACE USERNAME
order by
    pg_namespace.nspname
  , pg_class.relname
;

r -- SELECT ("read")
      w -- UPDATE ("write")
      a -- INSERT ("append")
      d -- DELETE
      D -- TRUNCATE
      x -- REFERENCES
      t -- TRIGGER
      X -- EXECUTE
      U -- USAGE
      C -- CREATE
      c -- CONNECT
      T -- TEMPORARY
arwdDxt -- ALL PRIVILEGES (for tables, varies for other objects)
      * -- grant option for preceding privilege

  /yyyy -- role that granted this privilege

import psycopg2

# Connect to Redshift
conn = psycopg2.connect(host="", dbname="", user="", password="", port="5439")
conn.autocommit = True
cursor = conn.cursor()

# List of users to drop
users = ['user_to_drop_1', 'user_to_drop_2']

# New owner, used when changing ownership
new_owner = 'new_user'

# Templates to change ownership, revoke permissions, and drop users
change_ownership = "select 'alter table '+schemaname+'.'+tablename+' owner to %s;' from pg_tables where tableowner like '%s'"
revoke_schema_permissions = "select distinct 'revoke all on schema '+schemaname+' from %s;' from admin.v_get_obj_priv_by_user where usename like '%s'"
revoke_table_permissions = "select distinct 'revoke all on all tables in schema '+schemaname+' from %s;' from admin.v_get_obj_priv_by_user where usename like '%s'"
drop_user = "drop user %s;"

for user in users:
    # Change ownership
    cursor.execute(change_ownership % (new_owner, user))
    for r in cursor.fetchall():
        print("Executing: %s" % r[0])
        cursor.execute(r[0])
    # Revoke schema permissions
    cursor.execute(revoke_schema_permissions % (user, user))
    for r in cursor.fetchall():
        print("Executing: %s" % r[0])
        cursor.execute(r[0])
    # Revoke table permissions
    cursor.execute(revoke_table_permissions % (user, user))
    for r in cursor.fetchall():
        print("Executing: %s" % r[0])
        cursor.execute(r[0])
    # Drop user
    cursor.execute(drop_user % (user))