Implement a basic reactive system.
Reactive programming is a programming paradigm that focuses on how values are computed in terms of each other to allow a change to one value to automatically propagate to other values, like in a spreadsheet.
Implement a basic reactive system with cells with settable values ("input" cells) and cells with values computed in terms of other cells ("compute" cells). Implement updates so that when an input value is changed, values propagate to reach a new stable system state.
In addition, compute cells should allow for registering change notification callbacks. Call a cell’s callbacks when the cell’s value in a new stable state has changed from the previous stable state.
Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message.
To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
raise Exception, you should write:
raise Exception("Meaningful message indicating the source of the error")To run the tests, run pytest react_test.py
Alternatively, you can tell Python to run the pytest module:
python -m pytest react_test.py
-v: enable verbose output-x: stop running tests on first failure--ff: run failures from previous test before running other test cases
For other options, see python -m pytest -h
Note that, when trying to submit an exercise, make sure the solution is in the $EXERCISM_WORKSPACE/python/react directory.
You can find your Exercism workspace by running exercism debug and looking for the line that starts with Workspace.
For more detailed information about running tests, code style and linting, please see Running the Tests.
It's possible to submit an incomplete solution so you can see how others have completed the exercise.