When I was a kid I loved video games. Now … we’re talking about 70s and 80s games: my first home computer was a Texas Instruments TI-99/4A, my second one a Commodore 64. I loved all games in those days, no matter how primitive they might seem like now; you can get a glimpse of WHAT we are talking about in this video. And funny enough, I still really do love them; below is one of my favorites, H.E.R.O. which I can play these days thanks to a C64 emulator.

Unfortunately for me, I did not catch (not then, at least) the programming bug. What really turned me down was having tried to type thousands of lines of BASIC to run what looked like an awesome adventure game from a command list in a magazine, only to never be able to play the game because the list was full of typos.

So, I want to make it better for both my daughter, AND myself,  because I plan to make more games. First of all, we are working with Python. There are a lot of resources for making games in Python; a really good one is Al Sweigart‘s Invent Your Own Computer Games with Python (as an aside: I have been using a chapter here, a chapter there from many of his books, it is awesome that he made them available online, but it was time to give back so I bought the 4th edition of Invent Your Own Computer Games with Python).

To set the stage for our first game I reviewed the first few chapters of the book, particularly Chapter 5: Dragon Realm, to get some ideas on how to use Python to make interactive games, but then decided to start with our own game: a calculator that would talk to the player, via the terminal, and ask for numbers and for their favorite algebraic operation. However, we added a twist because it sounded a lot more fun: IF her mom were to play, we’d want the results to be occasionally wrong. My daughter worked out some of the logic, after suggesting the twist, and I did the heavy lifting with Python; in the remainder of the post I will work through how we did it. Please note this game is written for Python 3.

In the first block, Jester, the calculator, introduces itself and then asks the player for their name; the name is stored to a variable via the input function and used for greeting and throughout the game. The capitalize() method turns the first letter of the name string to upper case, if needed.

print ('Hello, I am a talking calculator and my name is Jester.') 
name = input('What is your name? ') 
print ('Hello ' + name.capitalize() + ', nice to meet you!')

The real game starts in the big block below:

while True:
  operation = input(name.capitalize() + 
', would you like to add or subtract? (enter "a" or "s"; "q" to quit) ')
  if operation.lower() =='q':
    print('Goodbye ' + name.capitalize())
    break
  elif operation.lower() =='s' or operation.lower() =='a':
    print ('OK, ready.')
    input1 = input('Can I have the first number? ')
    try:
        num1=int(input1)
    except ValueError:
        print ("That is not a number!")
        input1 = input('Can I have the first number? ')
    input2 = input('Can I have the second number? ')
    try:
       num2=int(input2)
    except ValueError:
        print("That is not a number!")
        input2 = input('Can I have the second number? ')
    num1=int(input1)
    num2=int(input2)

Let’s break it up. First, the player chooses an operation (addition or subtraction) again via the input function. The while loop allows the player to continue playing after each operation.

while True:
  operation = input(name.capitalize() + 
', would you like to add or subtract? (enter "a" or "s"; "q" to quit) ')

The following if statement is used to exit the while loop (using break) if the player decides to quit.

  if operation.lower() =='q':
    print('Goodbye ' + name.capitalize())
    break

An elif statement comes next, allowing the player to chose the operation; at the same time if neither ‘a’ nor ‘s’ are chosen, the program will go back to the beginning of the while loop.

  elif operation.lower() =='s' or operation.lower() =='a':
    print ('OK, ready.')

Finally, Jester asks for the first number to be added or subtracted. We want to be sure that the string passed by the user in here is a number, so we use a try clause to handle a possible exception (for example a letter is entered instead of a number). Here is the logic: if when prompted for the first number we typed a letter by accident (for example the string ‘w’, instead of the string ‘3’ , when input1  is passed to int we’d get this fatal error and the program would be interrupted:

>>> num1=int(input1)
>>> ValueError: invalid literal for int() with base 10: 'w'

With the try clause we instead handle the exception by printing the custom error message “That is not a number!“, followed by a new request for a number:

    input1 = input('Can I have the first number? ')
    try:
        num1=int(input1)
    except ValueError:
        print ("That is not a number!")
        input1 = input('Can I have the first number? ')
    num1=int(input1)

The above cycle is repeated for the second number. After Jester gets two legitimate integers to work with, the operation part begins, which includes Jester’s prank. Indeed, depending on the name of the player, the result will be either always correct, or sometimes correct, sometimes a bit off (which is done using random). We picked “Olivia” to represent the “lucky” object of the prank. This is the only hard-coded part of the program. It needs to be changed with the name of the intended “victim”.

There are two nested if statements below that allow for the following to happen: if the player’s name is Olivia, a random number between 1 and 3, rand1 is drawn.  Then the  value of rand1 is checked: if if it is 3 then a non-zero number, num3, of value drawn between 1 and 5 (rand2) will be added to the result of the operation to make it wrong; otherwise the operation will execute correctly.

from random import randint
num3 = 0 # initializes random error variable
  if (name.lower() == 'olivia'): # for this player ....
    rnd1 = randint(1,3)
    rnd2 = randint(1,5)
    if rnd1 == 3: # .... if a 3 is drawn the correct result 
      num3 = rnd2 # .... will be modified by this random amount

Finally, this is the addition and subtraction block: in both cases unless “Olivia” is the player num3 will be zero and the result will be correct.

  if operation.lower() == 'a':
    result = num1 + num2 + num3
    print (str(num1) + ' + '  + str(num2) + ' = ' + str(result))
  elif operation.lower() == 's':
    result = (max(num1, num2) - min(num1, num2)) - num3
    print (str(max(num1, num2)) + ' - ' 
         + str(min(num1, num2))  + ' = ' + str(result))

If you want to play the game, please copy the full program below and paste it in a .py file and give it a try. Enjoy!

# NB optimized for Python 3
from random import randint

print ('Hello, I am a talking calculator and my name is Jester.')
name = input('What is your name? ')
print ('Hello ' + name.capitalize() + ', nice to meet you!')

while True:
  operation = input(name.capitalize() +
  ', would you like to add or subtract? (enter "a" or "s"; "q" to quit) ')

  if operation.lower() =='q':
    print('Goodbye ' + name.capitalize())
    break

  elif operation.lower() =='s' or operation.lower() =='a':
    print ('OK, ready.')
    input1 = input('Can I have the first number? ')
    try:
        num1=int(input1)
    except ValueError:
       print ("That is not a number!")
       input1 = input('Can I have the first number? ')

    input2 = input('Can I have the second number? ')
    try:
       num2=int(input2)
    except ValueError:
        print("That is not a number!")
        input2 = input('Can I have the second number? ')

    num1=int(input1)
    num2=int(input2)

  num3 = 0
  if (name.lower() == 'olivia'):
    rnd1 = randint(1,3)
    rnd2 = randint(1,5)
    if rnd1 == 3:
      num3 = rnd2

  if operation.lower() == 'a':
    result = num1 + num2 + num3
    print (str(num1) + ' + '  + str(num2) + ' = ' + str(result))

  elif operation.lower() == 's':
    result = (max(num1, num2) - min(num1, num2)) - num3
    print (str(max(num1, num2)) + ' - '
           + str(min(num1, num2))  + ' = ' + str(result))