re.split('[+ -]'，f)或更好地处理偏导数

I have been running in circles on some basic stuff. My idea is the following: I want to write a simple def , to do partial derivatives. I know there are tools out there already, but I happen to be an egotist with presumably bad antiquated python skills. without further ado, here is the situation. First the strategy: I want to split something like 2x + 3y into [2x , 3y]; then act on 2x , thus [0] and 3y, [1] with a derivative operation which I have not written yet. I plan on doing this symbolically. I have decided not to look into too much detail on how others have done it without trying a few dirty attempts. Here is my non working implentationI have been running in circles on some basic st