Kik bot made using Flask
You could just build a dictionary mapping classes to functions to call:

class A:
    pass

class B:
    pass

def func_a(x, y):
    return x + y

def func_b(x, y):
    return x - y

if __name__ == "__main__":
    d = {LinkMessage: link_message,
         PictureMessage: picture_message,
         VideoMessage: video_message,
         StartChattingMessage: chatting_message,
         ScanDataMessage: data_message,
         StickerMessage: sticker_message}
    message = PictureMessage()
    funcs[message.__class__]()


Alternatively, if these classes are controlled by you, you could give them all a method called the same name which will be called, maybe handle_message:

class LinkMessage:
    ...
    def handle_message(self, *args):
        pass

if __name__ == "__main__":
    message = LinkMessage()
    message.handle_message(1, 2)