on perhaps unloading modules?

[Hope Rouselle]

Greg Ewing <greg.ewing at canterbury.ac.nz> writes:

> On 21/08/21 6:15 am, Hope Rouselle wrote:
>>>>> code()
>> 'def p():\n  import math\n  return math.e\n'
>>>>> exec(code())
>>>>> p
>> <function p at 0x0113F5D0>
>>>>> p()
>> 2.718281828459045
>
> Note that this pollutes the globals of the module that you're calling
> exec() from. For better isolation you can pass in an explicit globals
> dict:
>
> g = {}
> exec(code(), g)
> g['p']()

Oh!  Now I understand how to use it!  That's in fact what I was looking
for.  I noticed it was polluting my environment and was thinking --- hm,
that's no good.  Thank you.

So I believe I understand how to pollute their environment too.  Say I
have a procedure called external that I'd like to make available to
them.  It seems this is what I need to do.

--8<---------------cut here---------------start------------->8---
def external():
  return "external"

def run():
  s = """
def s(*args):
  import math
  return external(), math.e, args
"""
  g = {}
  exec(s, g)
  g["external"] = external
  return g
--8<---------------cut here---------------end--------------->8---

>>> student["s"](1, 2)
('external', 2.718281828459045, (1, 2))

That's good.  So I can restrict their environment too, by removing some
built-ins and so on.  (I wish I could restrict their syntax too, though,
but I fear that's not possible.  For instance, it would be very useful
if I could remove loops.  If the course doesn't let them use them, it is
silly to have to ask them kindly not to use them --- please be patient
with this poorly designed course.  In reality there is a whole
department learning to run a course and there are many students helping
this department get a passing grade into how to do it.) :-D

Anyhow, your ideas have improved the outlook of this grader quite a lot.
Thank you!