Python code evaluation system and submissions server capable of unit tests, tracing, and AST inspection. Server can run on Python 2.7 but evaluation requires 3.7+.
Project description
potluck
Code for automatically evaluating Python programming tasks, including a
flask
WSGI server for handling submissions.
Specifications API design by Peter Mawhorter.
Server design by Peter Mawhorter, Scott Anderson, and Franklyn Turbak.
Based on codder
program by Ben Wood w/ contributions by Franklyn Turbak
and Peter Mawhorter.
Dependencies
The core evaluation code depends on the jinja2
, pygments
, markdown
,
importlib_resources
, beautifulsoup4
, and python_dateutil
packages.
Optional dependencies (get them using e.g., python -m pip install potluck-eval[test]
):
[test]
: Tests depend onpytest
, and you can run them usingtox
if you want.[expectations]
: Integration withoptimism
is available to require and grade student unit tests.[turtle_capture]
: Full support for capturingturtle
drawings requires thePillow
package (version 6.0.0 or later), as well as a Ghostscript installation (which is not simply a PyPI package and needs to be installed manually). Support for other image-producing code is possible, but would also requirePillow
.[synth]
: Integration withwavesynth
is available for capturing audio produced by that package. Support for other audio libraries is not built in but is possible.[server]
: If you want to run thepotluck_server
WSGI app, you'll needflask
andflask_cas
. If you're running the WSGI app on a server without a windowing system but still want to be able to evaluate submissions that use graphics (notably submissions which use theturtle
module), there is support for usingxvfb-run
(which would have to be installed separately as it's not a PyPI package).[security]
For full server security, you should also installflask_talisman
, andflask_seasurf
, but these are not required for running the server and won't be used if they're not present (although this introduces some extra security vulnerabilities).[https_debug]
If you want to use a self-signed certificate for HTTPS while hosting the WSGI server locally for debugging purposes, you'll needpyopenssl
. This is inconvenient, so it's not recommended unless you want to develop the server side of things.[formatting]
For better formatting of markdown instructions,pymarkdown-extensions
can be installed; it will be used if present, and the most important feature it provides is indented fenced code blocks so that they can be placed into list items.
Installing
To install from PyPI, run the following command on the command-line:
python3 -m pip install potluck-eval
Confirm installation from within Python by running:
>>> import potluck
Once that's done, you can perform run the built-in tests on the command-line:
python -m potluck.tests
Note that if you get a command not found error, the potluck_eval
script
might not have been installed somewhere that's on your command line's
path, which you'll need to fix to get the tests to run.
If you want to see what evaluation looks like yourself instead of just
running automated tests that clean up after themselves, in your installed
potluck
directory inside of site-packages
there's a testarea
directory; inside testarea/test_course/fall2021
you should be able to
run the following commands:
potluck_eval -t functionsTest --rubric
potluck_eval -t functionsTest --instructions
potluck_eval -t functionsTest -u perfect
potluck_eval -t functionsTest -u imperfect
potluck_eval -t functionsTest --check
The first command creates a rubric for the "functionsTest" task in the
rubrics
directory, and the second creates instructions in the
instructions
directory. The third and fourth commands will evaluate the
provided test submissions for the same task, creating reports as
reports/(im)perfect/functionsTest_TIMESTAMP.html
where TIMESTAMP is a
time-stamp based on when you run the command. The fifth command runs the
specification's built-in tests and prints out a report.
If the tests pass and these commands work, then potluck
is properly
installed and you can start figuring out how to set up your own
evaluation area and define your own tasks. The documentation for the
potluck.specifications
module describes the task-definition process and
provides a worked example that shows off many of the possibilities; you
can find that example specification at:
potluck/testarea/test_course/fall2021/specs/functionsTest/spec.py
Evaluation Setup
Once potluck
is installed and working , you'll need to set up your own
folder for evaluating submissions. The potluck/testarea
folder contains
an example of this, including task specifications and example
submissions (note that it's missing a submissions
folder because all of
its submissions are examples, as the potluck_config.py
there notes).
You can test things out there, but eventually you'll want to create your
own evaluation directory, which should have at minimum:
tasks.json
: This file specifies which tasks exist and how to load their specifications, as well as which submitted files to look for and evaluate. You can work from the example inpotluck/testarea/test_course/fall2021/tasks.json
.- A
specs
folder with one or more task sub-folders, named by their task IDs. Each task sub-folder should have aspec.py
file that defines the task, as well asstarter/
andsoln/
folders which hold starter and solution code. These files and folders need to match what's specified intasks.json
. - A
submissions
folder, with per-user submissions folders containing per-task folders that have actual submitted files in them. Note that if you're going to use thepotluck_server
WSGI app, this can be created automatically.
If you're going to use the potluck_server
WSGI app, your evaluation
directory will also need:
potluck-admin.json
: Defines which users have admin privileges and allows things like masquerading and time travel. Work from the provided examplepotluck/testarea/test_course/fall2021/potluck-admin.json
.
Finally, to run automated tests on your specifications (always a good idea) you will need:
- An
examples
folder with the same structure as thesubmissions
folder.
Running potluck_server
To set up potluck_server
, in addition to an evaluation directory set up
as described above, you'll need to create a ps_config.py
file in a
directory of your choosing (could be the same as the base evaluation
directory if you want); there's a rundir
directory inside the installed
potluck_server
directory which has an example of this; in addition to
ps_config.py
, secret
and syncauth
files will be created in the
server run-directory if not present.
For testing purposes, you will not need to change the ps_config.py
file
from the defaults supplied in ps_config.py.example
, but you'll want to
edit it extensively before running the server for real. When running in a
real WSGI context, you'll also need the potluck.wsgi
file that's
present in the potluck_server/rundir
directory.
Once ps_config.py
has been created, from the potluck_server/rundir
directory (or whatever directory you set up) you should be able to run:
python -m potluck_server.app
to run the WSGI app on a local port in debugging mode. It will print several messages including one or more prompts about running without authentication, and you'll have to press enter at these prompts to actually start the server, after which it should provide you with a link you can use in a browser to access it.
NOTE THAT THE POTLUCK WEB APP ALLOWS AUTHENTICATED USERS TO RUN ARBITRARY PYTHON CODE ON THE SERVER!
In addition to this, in debugging mode the server has no authentication,
and is only protected by the fact that it's only accessible to localhost.
Accordingly, you will need to set up CAS (Central Authentication Server)
via the values in ps_config.py
to run the server for real. If you don't
have access to a CAS instance via your company or institution, you can
either set one up yourself, or you'll have to modify the server to use
some other form of authentication. It is also strongly recommended that
you install the flask_talisman
and flask_seasurf
modules, which will
be used to provide additional security only if they're available. If
pyopenssl
is installed alongside flask_talisman
, a self-signed
certificate will be used to provide HTTPS even in debugging mode, mostly
just to maximize similarity between debugging & production environments.
In debugging mode, you will automatically be logged in as the "test"
user, and with the default potluck-admin.json
file, this will be an
admin account, allowing you to do things like view full feedback before
the submission deadline is past. With the default setup, you should be
able to submit files for the testing tasks, and view the feedback
generated for those files (eventually, you may have to modify the due
dates in the example tasks.json
for this to work). You can find files
to submit in the potluck/testarea/test_course/fall2021/submissions
directory, and you can always try submitting some of the solution files.
See the documentation at the top of python_server/app.py
for a run-down
of how the server works and what's available.
To actually install the server as a WSGI app, you'll need to follow the
standard procedure for whatever HTTP server you're using. For example,
with Apache, this involves installing mod_wsgi and creating various
configuration files. An example Apache mod_wsgi configuration might look
like this (to be placed in /etc/httpd/conf.d
):
# ================================================================
# Potluck App for code submission & grading (runs potluck_eval)
# the following is now necessary in Apache 2.4; the default seems to be to deny.
<Directory "/home/potluck/private/potluck/potluck_server">
Require all granted
</Directory>
WSGIDaemonProcess potluck user=potluck processes=5 display-name=httpd-potluck home=/home/potluck/rundir python-home=/home/potluck/potluck-python python-path=/home/potluck/rundir
WSGIScriptAlias /potluck /home/potluck/rundir/potluck.wsgi process-group=potluck
Security
Running the potluck_server WSGI app on a public-facing port represents a significant security vulnerability, since any authenticated user can submit tasks, and the evaluation mechanisms currently do not use any sandboxing, meaning that they RUN UNTRUSTED PYTHON CODE DIRECTLY ON YOUR SERVER (even if they used sandboxing, which is a target feature for the future, they would be vulnerable to any means of circumventing the sandboxing used).
You therefore need to trust that your CAS setup is secure, and trust that your users will be responsible about submitting files and about keeping their accounts secure. If you can't depend on these things, DO NOT run the web app.
Even if you do not run the web app, and instead collect submissions via some other mechanism, the evaluation machinery still runs submitted code directly. You will need to trust the users submitting tasks for evaluation, and watch out for accidental mis-use of resources (e.g., creating files in an infinite loop). It's not a bad idea to run the entire evaluation process in a virtual machine, although the details of such a setup are beyond this document.
Documentation
Extracted documentation can be viewed online at: https://cs.wellesley.edu/~pmwh/potluck/docs/potluck/
You can also read the same documentation in the docstrings of the source
code, or compile it yourself if you've got make
and pdoc
installed by
running the make docs
script on the command-line (note that shenanigans
are necessary to prevent pdoc from trying to import the test
submissions).
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