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13.2. Comparing Strings

We can also work with user input directly in string form. If the user is supposed to enter a word or other piece of text, it makes no sense to try to convert that to a number. Fortunately, the comparison operators like ==, !=, >, etc… all work with strings.

This program is something like we might have in part of a text based adventure game where the user is trying to navigate a maze:

print("You are in front of a creepy door in a hallway.") print("What do you want to do?") action = input("Type: in, left, or right. Then click OK or press enter") if action == "in": print("You choose to go in.") print("The room is pitch black.") elif action == "left": print("You choose to turn left.") print("A ghost appears at the end of the hall.") elif action == "right": print("You choose to turn right.") print("A greenish light is visible in the distance.")

What is the printed if the user answer something other than in, left, or right?

• The room is pitch black.
• This line will be printed when the user enters in.
• A ghost appears at the end of the hall.
• This line will printed when the user enters left.
• A greenish light is visible in the distance.
• This line will printed when the user enters right.
• None of the above is printed.
• None of the conditions will be true if the user enters something other than in, left, or right so none of these will be printed.

Now it is your turn to write a program that makes decisions with strings. In the program below, you job is to write the function that will turn a letter grade like “A” into the GPA points it is worth: 4. That function will be used to calculate the GPA of someone who took three classes.

Notice that there is some commented out code that hardcodes in three input values. Hardcoded values are ones that are written into a program instead of coming from outside as the program runs (like from user input). Sometimes, hardcoding some values makes it easier to test a function like the one you need to write - you can run the program and immediately see the result instead of having to type in all the inputs every time you run it. Then, once you get the function working, you can remove the hardcoded values and start using real input.

Write the code for the getGPAPoints function. It should return the GPA points for the given letterGrade. An "A" should result in 4, a "B" in 3, a "C" in 2, a "D" in 1, and an “F” in 0.

def getGPAPoints(letterGrade): #write funciton code here # Main part of program letter1 = input("Enter your first grade") letter2 = input("Enter your second grade") letter3 = input("Enter your third grade") # Hard coded values to test with. You can comment out the lines above # and uncomment these three lines to make it easier to test your code. # letter1 = "A" # letter2 = "C" # letter3 = "A" totalPoints = getGPAPoints(letter1) + getGPAPoints(letter2) + getGPAPoints(letter3) gpa = totalPoints / 3 print("Your GPA is", gpa) ===== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(getGPAPoints("A"), 4, "Testing output for A.") self.assertEqual(getGPAPoints("B"), 3, "Testing output for B.") self.assertEqual(getGPAPoints("C"), 2, "Testing output for C.") self.assertEqual(getGPAPoints("D"), 1, "Testing output for D.") self.assertEqual(getGPAPoints("F"), 0, "Testing output for F.") myTests().main()

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