Practice Python

Exercise

Make a two-player Rock-Paper-Scissors game. (Hint: Ask for player plays (using input), compare them, print out a message of congratulations to the winner, and ask if the players want to start a new game)
Remember the rules:

• Rock beats scissors
• Scissors beats paper
• Paper beats rock

Discussion

Concepts for this week:

• While loops
• Break statements

While loops

We have already discussed for loops, or loops that look sequentially (one by one) at elements in a list. There is a second type of loop that works in a slightly different way called a while loop.
The idea is simple: while a certain condition is True, keep doing something. For example:

a = 5
while (a > 0):
    print(a)
    a -= 1

The output of this code segment is:

5
4
3
2
1

A particularly useful way to use while loops is checking user input for correctness. For example:

quit = input('Type "enter" to quit:' )
while quit != "enter":
    quit = input('Type "enter" to quit:' )

The uses for this are infinite, and can (and should!) be combined with conditionals to yield the most efficient results.

Break statements

A break statement stops the execution of a loop before the original condition is met. While the use of a break statement will often start an argument about good coding practices, sometimes it is useful.
For example:

while True: 
    usr_command = input("Enter your command: ")
    if usr_command == "quit":
        break
    else: 
        print("You typed " + usr_command)

In this case, the break statement is used to break off the "infinite while loop" that we have constructed with the while True statement.

Happy coding!
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