<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def create_app():
 """Flask application factory function."""

    app = Flask(__name__)
    app.config_from_envvar = app.config.from_envvar
    app.config_from_object = app.config.from_object
    configure_app(app)
    init_core(app)
    register_blueprints(app)
    return app