def run_migrations_offline():
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    connectable = config.attributes.get('connection', None)
    config_opts = {}
    config_opts.update(common_config_opts)
    config_opts["literal_binds"] = True

    if connectable is None:
        config_opts["url"] = config.get_main_option("sqlalchemy.url")
    else:
        config_opts["connection"] = connectable
    context.configure(**config_opts)

    with context.begin_transaction():
        context.run_migrations()
Run migrations in 'offline' mode.

This configures the context with just a URL
and not an Engine, though an Engine is acceptable
here as well.  By skipping the Engine creation
we don't even need a DBAPI to be available.

Calls to context.execute() here emit the given string to the
script output.
jupyterhub/alembic/env.py