We describe here a very simple method that enables us to autocorrect student submitted python programs, in the context of a first programming course at University level.

This method is not automated as much as it could be, but it is very easy to set up and extremely flexible.

Each assigned problem (program to be written) is created by the teacher in one directory. This directory will contain three files, at least:

One can see two examples of such problems at

• myuser.py:
  This is the program as solved by the teacher. This file is rich in comments which explain to the student what the specific problem asks for, giving examples etc. The teacher solution, usually the code of a function or two, is specified in two lines starting with START and STOP. Input/output is usually handled outside the START/STOP lines, so the student does not have to deal with I/O at all, and only has to write code that computes something.
  This file is hidden from the students, either by restricting read permissions on the server or by not inluding it in the directory given to the students.
  When creating a new problem, this is the file that the teacher first writes, usually by suitably modifying a previously used myuser.py file.
• user.py:
  This is derived from myuser.py by erasing the code written by the teacher that the student is supposed to come up with. In other words, the code written by the teacher between the START and STOP lines is erased, and the student must write his own code between these two lines, and only there.
• tester.py:
  This is a teacher supplied program that tests the student's user.py program for correctness by trying it on a few cases.
  After the teacher has created file myuser.py he creates the tester by modifying a previously used tester.py file.

The workflow of the student is as follows:

• The student creates an empty directory for the problem and downloads the correspoding user.py and tester.py files in there.
• The student edits user.py, reads the description of the problem therein and writes the code necessary between the START and STOP lines. The user tests his program by giving the command

  python user.py

  and inspecting the results. The user repeats until satisfied that the program is correct.
• The student tests his program also with the tester:

  python tester.py

  If any of the test cases leads to an error the student goes back to the previous step.
• The student submits the file user.py to be graded. How this is done depends on the implementation. It could be by uploading the file to a server, by emailing the teach with the file, or by other means.

For correction the teacher adds one or two more cases to his copy of the tester (to defeat students who might cheat by looking into their tester and make their program return the corresponding outputs for each value of the input listed in there) and uses a script to apply the tester to each submitted program and record the results to a file or database.