h2m | Tool for converting HTML to Markdown , like html2markdown

I have created a script that allows me to periodically send multiple reminders in the form of Windows Desktop notifications at set intervals, without conflicting with each other. I did this by creating a LockedNotifier class that creates a win10toast toast notification with the process requiring a lock to prevent race conditions. I then have a 'MultiToast' class which uses a multitimer to repeatedly call the notifier class method and stores all of the parameters for Multitimer and ToastNotifier() functions as members. My code is as follows:

I need to obtain a derivative to use it later in numerical calculations. And my code doesn't work at all. I tried to use lambdify but the error is "can't convert symbols int". I read other answers for similar questions but it still doesn't work.

I am trying to convert buffer image to opencv mat by mat.at(i,j),but it runs 20 ms .It's too slow.How to improve the speed ?or another method to convert buffer image to cv::Mat?