How can i make Drag and drop flowchart in Python or Kivy

As in the title i want to make an app and in this app users can create their flowchart. I want to develop this app for mobile phones.
For example

I think for the start i need to do connect A and B blocks by dragging them from their edge like this:

But i dont know how to do it
Which python module should i use ? I did GUI with kivy and i need help for this