Have submitted notebooks import from local directory

[Kevin Yang]

I had students edit a python file and then submit it along with the notebooks. However, when I run the autograder, nbgrader imports the python file from my source directory instead of the submitted one. This, of course, leads to the test cells that test their implementation always passing no matter what they do (and also makes it so that, if they added and rely on any further functionality that's not in my solution, then those blocks fail!). Is there any way to have the submitted notebooks import from the submitted .py file?