错误日志如下，代码是copy《flask web 开发》

lanxiang@machine:~/bushu2$ heroku run python manage.py deploy
Running python manage.py deploy on ⬢ x1996... up, run.8593
INFO  [alembic.migration] Context impl PostgresqlImpl.
INFO  [alembic.migration] Will assume transactional DDL.
INFO  [alembic.migration] Running upgrade None -> f3893df0869f, init migrations
Traceback (most recent call last):
  File "manage.py", line 81, in <module>
    manager.run()
  File "/app/.heroku/python/lib/python2.7/site-packages/flask_script/__init__.py", line 405, in run
    result = self.handle(sys.argv[0], sys.argv[1:])
  File "/app/.heroku/python/lib/python2.7/site-packages/flask_script/__init__.py", line 384, in handle
    return handle(app, *positional_args, **kwargs)
  File "/app/.heroku/python/lib/python2.7/site-packages/flask_script/commands.py", line 145, in handle
    return self.run(*args, **kwargs)
  File "manage.py", line 71, in deploy
    upgrade()
  File "/app/.heroku/python/lib/python2.7/site-packages/flask_migrate/__init__.py", line 98, in upgrade
    command.upgrade(config, revision, sql = sql, tag = tag)
  File "/app/.heroku/python/lib/python2.7/site-packages/alembic/command.py", line 124, in upgrade
    script.run_env()
  File "/app/.heroku/python/lib/python2.7/site-packages/alembic/script.py", line 199, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "/app/.heroku/python/lib/python2.7/site-packages/alembic/util.py", line 199, in load_python_file
    module = load_module(module_id, path)
  File "/app/.heroku/python/lib/python2.7/site-packages/alembic/compat.py", line 55, in load_module
    mod = imp.load_source(module_id, path, fp)
  File "migrations/env.py", line 72, in <module>
    run_migrations_online()
  File "migrations/env.py", line 65, in run_migrations_online
    context.run_migrations()
  File "<string>", line 7, in run_migrations
  File "/app/.heroku/python/lib/python2.7/site-packages/alembic/environment.py", line 652, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/app/.heroku/python/lib/python2.7/site-packages/alembic/migration.py", line 225, in run_migrations
    change(**kw)
  File "migrations/versions/f3893df0869f_init_migrations.py", line 27, in upgrade
    op.create_index(op.f('ix_roles_default'), 'roles', ['default'], unique=False)
AttributeError: 'module' object has no attribute 'f'