Introduction to Computer Science and Programming in Python

Lecture 7

1. Black Box and Glass Box Testing

   With the below implementation, is the test set “n = 4 | n = -4 | n = 5” path complete?

   def is_even(n):
       """ 
       Returns True if a number is even
       and False if not 
       """
       if n > 0 and n % 2 == 0:
           return True
       elif n < 0 and n % 2 == 0:
           return True
       else: 
           return False
   

   Yes check

   No close

   Check

   With the above implementation, which value for n is incorrectly labeled by is_even?

   n is very large (and positive) close

   n is very small (and negative) close

   n is 0 check

   Check   Show Solution

2. Errors

   Below is a piece of code and an error shown when running it. What is the problem?

   L = 3
   for i in range(len(L)):
       print(i)
   
   ERROR MESSAGE:
   
    File "C:/Users/Ana/.spyder2-py3/temp.py", line 2, in 
       for i in range(len(L)):
   
   TypeError: object of type 'int' has no len()
   

   You are not allowed to name an integer with the variable name L close

   range is not allowed to have an expression inside its parentheses close

   You are not allowed to call len on an integer check

   You are not allowed to print the loop variable i close

   Check   Show Solution

3. Exceptions

   If the user enters “twenty” in the code below what does the program do?

   try:
       n = int(input("How old are you? "))
       percent = round(n*100/80, 1)
       print("You've gone through", percent, "% of your life!")
   except ValueError:
       print("Oops, must enter a number.")
   except ZeroDivisionError:
       print("Division by zero.")
   except:
       print("Something went very wrong.")
   

   prints “You’ve gone through 25.0 % of your life!" close

   prints “Oops, must enter a number." check

   Check

   If the user enters “0” in the code above what does the program do?

   prints “You’ve gone through 0.0 % of your life!" check

   prints “Division by zero." close

   Check   Show Solution