Due Saturday, Oct 10, before midnight

At the end of your lab session, be sure to run handin21.

Your lab instructor will check your files, which should reflect that you have made non-trivial progress (in python or pseudocode) towards the solution. Note that if you have not made much progress towards your solution, we expect that you would have been actively seeking help during your lab over Slack.

A portion of your final lab grade is dependent on this checkpoint.

If there are circumstances which prevent you from making substantial progress on this lab, please contact your lab instructor as soon as possible.

In this lab, we will be writing a program for a human user to play rock-paper-scissors against a computer. We will build this incrementally. As such, we’ll be modifying the main function as we move from step to step. There’s no need to save your main function from a previous step as you work on each next step.

In the file named rps.py, write a function named getChoice that asks a user to enter one of "rock", "paper", or "scissors", and returns the string value entered by the user. If the user doesn’t enter one of these three string values, your function should print an error message, and prompt the user to try again. The function should only return when the user enters a valid string value.

The getChoice function does not take any input values (it has no parameters), but it should return a string value. Its function definition will look like:

Your main function should make a call to the getChoice function and print out the value returned. Here are some examples of how the program should work:

Remember that python strings can be compared with relational operators like == or < just like integers and floats.

Let’s extend our program to add a function that plays one game of rock-paper-scissors.

Remember, we are solving this incrementally so there’s no need to preserve your main function as you develop the solution to this next step.

To play a game, add a new function called calculateWinner. This function takes as input two string values, the first representing player one’s choice (of "rock", "paper", or "scissors"), and the second representing player two’s choice. The function should determine the winner of one game of rock-paper-scissors based on the players' choices, and return a value indicating which player won. The function should return:

Its function definition will look like:

The rules of rock-paper-scissors are:

Here are some example runs:

For the final part, you are going to add code so that you can play multiple rounds of rock-paper-scissors against the computer. After each round of the game, you should print out the current scores using a function called printScores.

Be sure that all of the functions you write for this lab are well commented.

There’s no need to preserve your main function from the previous step, but much of what you wrote in the last step can be reused in this step if you find that helpful.

Each lab will have a short questionnaire at the end. Please edit the Questions-04.txt file in your cs21/labs/04 directory and answer the questions in that file.

Once you’re done with that, run handin21 again.

Remember to run handin21 to turn in your lab files! You may run handin21 as many times as you want. Each time it will turn in any new work. We recommend running handin21 after you complete each program or after you complete significant work on any one program.