import iofrom flask import current_app as appfrom flask import send_filefrom myproject import Obj@app.route('/logo.png')def logo():    obj = Obj.objects.get(title='Logo')    return send_file(io.BytesIO(obj.logo.read()),                     attachment_filename='logo.jpg',                     mimetype='image/jpg')

通过io.BytesIO 从二进制数据获取一个fd.