dlsys course repository.

1. Use pytest command line under homework/hw*
2. In pycharm, right click directory, "make directory as Source root" has influence on pytest, if do hw2, should Unmark other hw*.
3. Use vscode to write codes, and use pycharm to test or debug codes.
4. if get error ModuleNotFoundError: No module named 'needle', use command export PYTHONPATH=$PYTHONPATH:/home/zhuyangyang/Course/CMU10_414/homework/hw?/python, this will temporarily add the directory to the PYTHONPATH environment variable.
5. if use pycharm, make sure only make dir as source root that under current homework/hw*, and unmark dir as source root under other hw*.