Online tests

In most weeks there will be an online test in which you will be asked to enter some Python code. For example, a question might ask you to define a function add_forty_two(x) that accepts an argument $x$, adds $42$ to it, and returns the result. You would then enter the following code:

def add_forty_two(x):
    """Add 42 to x."""
    return x+42
   

• You should always write and test your code in VS Code first, and only paste it into the online test system when you are sure that it is correct.
• In almost all cases, the question will ask you to define one or more functions. Your answer should just consist of function definitions, without any other code (except possibly some import statements, as discussed below).
• The test system will only accept your code if it follows the specification precisely. It will not work to define a function AddFortyTwo(n) instead of add_forty_two(x), for example. (You should remember that precise compliance with a specification is very often necessary for your code to interact correctly with other code, so this is a very normal issue in software development.)
• The line """Add 42 to x.""" is a docstring. Unless otherwise specified, you should include a docstring for each function that you define. It needs to come directly after the function definition line.
• When developing your code, you might test it by adding print statements inside or outside the function definition, like this:

  
  def add_forty_two(x):
      """Add 42 to x."""
      print(f"Adding 42 to {x}")
      return x+42
  
  print(add_forty_two(1000))
       

  It is definitely a good idea to test your code like this, with a range of test cases. However, you should remove all print statements before pasting your code into the online test system. Unexpected print statements can cause the system to reject your code even if it is otherwise correct.
• The question may tell you that you can assume various things about the arguments to your function. For example, you might be asked to define add_forty_two(x) with the assumption that $x$ is an integer. You should then check that your function works correctly when $x$ is an integer, even if it is zero or negative, for example. However, you do not need to check that your function works correctly when $x$ is a string or a list or a dictionary or anything else.
• A few questions will ask you to plot something. However, you should not plot anything unless the question specifically asks you to, because that can cause various errors. Also, your code should not call plt.show(). (If you do things in the way that I will demonstrate in lectures then you will almost never call plt.show() anyway. There are various other ways of working that involve calling plt.show(), but that is not compatible with the online test system.)
• Sometimes you might need to include import directives at the top of your code; for example you might need import numpy as np to make the np.sqrt() function available. Each question will have instructions about this, which you should read carefully.
  • Some questions will disallow import directives, so you will need to solve the problem without using any external libraries.
  • Some questions will ask you to work out for yourself what import directives you need to include.
  • Many questions will tell you that certain libraries will be available (without you having to import them explicitly) and will tell you that you do not need to import anything else.
  In particular, you should not import matplotlib. If the question requires plotting, then matplotlib will be available to you without needing to import it. If the question is not set up for plotting, then importing matplotlib will cause an error.