import reimport sysfrom sqlalchemy import *from migrate import *from sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy.orm import relation, deferred, mapper, backrefBase = declarative_base()Base.metadata.bind = migrate_enginebad_characters = "<>| '\""invalid_chars = re.compile(r'[%s]' % bad_characters)class User(Base):    __tablename__ = "users"        id = Column(Integer, primary_key=True)    username = Column(String(128), unique=True)    email = Column(String(128))    password = Column(String(20))    settings = Column(PickleType())    projects = relation('Project', backref='owner')    quota = Column(Integer, default=10)    amount_used = Column(Integer, default=0)usertable = User.__table__changed_names = dict()def check_name(new_name):    result = select([func.count('*')]).where(usertable.c.username==new_name).execute()    row = result.fetchone()    return row[0]def upgrade():    # Upgrade operations go here. Don't create your own engine; use the engine    # named 'migrate_engine' imported from migrate.    for row in select([usertable.c.username]).execute():        name = row.username        if invalid_chars.search(name):            changed_names[name] = invalid_chars.sub("", name)    for old_name, new_name in changed_names.items():        if check_name(new_name):            print "%s is in use for %s" % (new_name, old_name)            new_name = invalid_chars.sub("-", old_name)            changed_names[old_name] = new_name            if check_name(new_name):                print "EVEN WORSE: %s is in use for %s also" % (new_name, old_name)                print "Can't continue"                sys.exit(1)    for old_name, new_name in changed_names.items():        update(usertable).where(usertable.c.username==old_name).execute(username=new_name)    def downgrade():    for old_name, new_name in changed_names.items():        update(usertable).where(usertable.c.username==new_name).execute(username=old_name)