seeding.rst

Seeding

An important aspect of writing code in the data science environment is the ability to simulate random processes. This presents a unique challenge to autograding assignments because the random state of the students' environments will be completely different from the grading environment. Some autograding solutions account for this issue by incorporating calls to seed random libraries during execution; Otter-Grader does this very easily using grading configurations, and this is by far the most preferable solution if you're using Otter.

When working with other autograding solutions, seeds must be incorporated into the test files themselves and assignments must be written in such a way as to make the seeding before execution possible.

Solution 1: Functions

The first and easiest solution to this problem is to have students wrap their code involving randomness into a function. In this way, the tests can make a seeding call before calling the function directly, ensuring that the seed set before the code is executed. Consider the following example question and the following test:

import numpy as np

# Question 1: Define roll_die which rolls a 6-sided die using NumPy.
def roll_die():
    return np.random.choice(np.arange(1, 7))

>>> np.random.seed(42)
>>> roll_die()
4

This approach, while easy-to-implement and effective, is generally at odds with the general autograding paradigm of testing global variables directly rather than encapsulting logic in needless functions. For this reason, there is another solution that is perhaps more elegant.

Solution 2: Seeding the Students' Code

In this solution, the random libraries are seeded directly before the student writes their code in a manner visible to the students.

import numpy as np

np.random.seed(42)

# Question 1: Assign roll_value to the roll of a six-sided die.
roll_value = np.random.choice(np.arange(1, 7))

>>> np.random.seed(42)
>>> roll_die()
4

This method is significantly less elegant and is susceptible to students changing the seed, which could throw off the results of the test and fail students incorrectly. It is also important to note that if you're working in a notebook format, you need to include seeds im every randomness cell because repeated runs of cells will change the seed value for subsequent questions, which could result in students failing tests.