Exceptions Activity

Wave 0: Setup

1. Have one team member fork AND clone this repository. They will be the driver. All commands and code will be run on their computer.

2. Make sure you do not have a virtual environment from another project active. We will create a new virtual environment for this activity.

3. Navigate to the activity directory and create a virtual environment inside it.

python3 -m venv venv

4. Activate the virtual environment.

source venv/bin/activate

5. Install requirements.

pip install -r requirements.txt

Wave 1: Understanding the code.

1. Run the code, entering a few numbers and computing an average.

python3 main.py

2. Read the code in average_calculator/calc.py, discussing with your group how it works. In particular, what is the try/except doing?

3. Predict what will happen if you run the code and try to compute an average before entering any numbers. Then, try actually running it. What happens? Does it match what you expected?

Wave 2: Raising a better exception.

1. Modify the average function. Make it so that it does NOT raise a ZeroDivisionError. Instead, have it raise a ValueError when an empty list is passed in. The description of the new error you create should be cannot compute average of an empty collection.

2. Run the code again, attempting to compute an average before entering any numbers. Verify that your new exception shows up.

3. Create a new commit with your changes added, and push it to GitHub.

Wave 3: Catching an exception.

1. Modify the calculator function, adding a new try/catch to catch your new exception. Make it so that the code does not crash if the user attempts to calculate an average before entering numbers. Instead, it should show the message You must enter at least one number before calculating an average. It should then continue to prompt the user for more input.

2. Create a new commit with your changes added, and push it to GitHub.

Wave 4: Tests

1. Verify that pytest is set up correctly by running pytest on the terminal (make sure you have your virtual environment activated!). You should see two tests skipped.

2. Open tests/test_calc.py and complete test_average_of_two_numbers_is_properly_computed. This does not require any exception handling. Unskip the test and verify that it works.

3. Complete test_average_of_empty_list_raises_ValueError. This does require testing for an exception. Unskip the test and verify that it works.

4. Create a new commit with your changes added, and push it to GitHub.

OPTIONAL Wave 5:

1. Add additional tests to more thoroughly test the code.

2. Try modifying the calculator function to instead use the "Look Before You Leap" strategy, so that you do not need to use a try/except for the average. Which style do you prefer? What are the tradeoffs between the two, especially when we imagine adding more and more code that uses these functions?