change the size of string column using sqlalchemy migrate

Why on earth have I done a table description like

CREATE TABLE address
(
  id serial NOT NULL,
  street text,
  city character varying(255),
  province character varying(10),
...

what a scrooge, 10 chars only, you can't live in saskatchewan with that. I had to migrate.

After a while I managed to get the syntax that makes it work

def upgrade(migrate_engine):
    meta.bind = migrate_engine
    address = Table('address', meta, autoload=True)
    address.c.province.alter(type=VARCHAR(length=255))