This is a known problem.... it stems from the fact that the various formgrader tools use regular expressions to separate the directory paths {course_directory}/{nbgrader_step}/{student_id}/{assignment_id}/{notebook_id}.ipynb (see https://nbgrader.readthedocs.io/en/stable/user_guide/philosophy.html#how-to-structure-course-files)

The characters [{(]})\?+. all have special meaning in regular expressions, so mess up that calculation.

@perllaghu Nevertheless, it should be fixed: every regex library has some escape function like re.escape() in Python.

I had a similar problem in the service I run..... but for course codes - fortunately I could control that: I swapped all brackets & slashes for a high-order Unicode equivalent - { -> ｛, for example.

This leaves the base nbgrader code-base unaffected, yet remains perfectly readable for the user.

[it did have an unfortunate side-effect: We support LTI connectivity & Grade Passback.... and abc (12/3) != abc（12∕3） - oops]

..... however, yes: fixing the annoying regex problem would be good.

Path escaping was added all the way back in 2016 (70d6c8f), but was set to False by default.

The code here is quite fishy to me, so I'm looking into why that might still be the case and see if we can't clean this up.