Quiz 3 Study Guide

Quiz 3 will be in class on Friday, October 28 at the start of class.

Python concepts

You are responsible for all material needed for Labs 1 through 6, which includes for loops, if statements, boolean operators, relational operators, logic operators, while loops, functions, and lists.

Study guides are not graded. You may work with other students on the questions, and ask questions about the guide during evening ninja help sessions, on Slack, or with meetings with faculty and staff. We do not provide full solutions to the study guides.

In addition to all concepts from Quiz 2, you should understand the following:

  • list data type

  • list manipulation (accumulators, indexing, etc)

  • mutable and immutable types

  • functions with returns and functions with side effects

    • stubbed-out (prototyped) function

Practice problems

  1. Write a program which asks the user for 4 words and then prints them in reverse order. Hint: store them in a list.

    Here’s an example run of the program:

    word 1: hello
word 2: zebra
word 3: unicorn
word 4: corgi
corgi
unicorn
zebra
hello

  2. Write a program that reads in student grades from the user, until the user enters a -1. After reading in the -1, the program should compute and display the average grade.

    Please enter your grades below.  Enter a -1 when you are all done

grade  1: 98
grade  2: 87
grade  3: 65
grade  4: 95
grade  5: 80
grade  6: -1

The average of those 5 grades is 85.000

  3. Analyze the following code:

    m = ["t","i","m","e"]
s = "time"
m[1] = "a"
s[1] = "a"

    What happens when this code is executed? What are the values of m and s afterward?

  4. Consider the following program:

    def is_odd(number):
   # Q1: draw stack here (the first
   #     time the function is called)
   if number % 2 == 0:
      return False
   else:
      return True

def enigma(ls):
   total = 0
   for i in range(len(ls)):
      if is_odd(ls[i]):
         ls[i] = ls[i]*2
      total = total + ls[i]
   return total

def main():
   values = [5,3,4,8]
   print(values)
   result = enigma(values)
   print("result: %d" % result)
   print(values)

main()

    1. Draw the function stack as it would look the first time is_odd() is called. [answer]

    2. What variables are in scope at this point in the code?

    3. What is the program’s output (i.e. what does it print when the program is run)?

    4. What does the enigma() function do?

  5. Write a function called get_int that has two parameters, lo and hi. The function should prompt the user to enter an integer between lo and hi (inclusive), and then return the value entered. Your function should not return until the user enters a valid integer in the range lo to hi. You may assume both lo and hi are positive integers.

    Now add a main() function that calls get_int to get an integer from 1-10. Your main() should then print out "Boo!" that many times.

    Here’s an example run of the full program:

    Please enter an integer from 1-10: 99
Please enter an integer from 1-10: -40
Please enter an integer from 1-10: 4
Boo!
Boo!
Boo!
Boo!

  6. For the following program, show the full output when the program is run to completion, and draw the stack as it would look just before the computer executes the return count statement.

    def update(L, S):
  count = 0
  data = S.split()
  for item in data:
    if item not in L:
      L.append(item)
      count = count + 1
  # draw stack here
  return count

def main():
  words = ['roses','are','red']
  print(words)
  line = 'violets are blue'
  result = update(words,line)
  print(result)
  print(words)

main()

  7. The following get_numbers(n) function doesn’t work. Find and fix the bug in the code below.

    def get_numbers(n):
    """
    Purpose: Read n numbers from the user and return them as a list
    Parameters: n -- the number of values to read from the user (integer)
    Return: a list of the numbers entered by the user
    """
    for i in range(n):
        value_list = []
        value = int(input("Enter a number: "))
        value_list.append(value)
    return value_list

  8. Consider the game Rock, Paper, Scissors. Assume you have these two functions already written:

    • getPick() asks the user for "r,p,s?" and returns:

      • "rock" if they enter r

      • "paper" if they enter p

      • "scissors" if they enter s

    • winner(user,comp) returns:

      • "user" if user won the game (e.g., user="rock", comp="scissors")

      • "comp" if comp won the game (e.g., user="rock", comp="paper")

      • "tie" if it’s a tie game (e.g., user="rock", comp="rock")

        Write a main() function that uses the above functions to play one round of rock-paper-scissors. Here are a few sample runs of the program:

        $ python3 rps.py
r,p,s?: r
Computer chose rock
tie...
$ python3 rps.py
r,p,s?: r
Computer chose paper
Computer wins!
$ python3 rps.py
r,p,s?: r
Computer chose scissors
You win!

  9. Write the stub for the winner(user, comp) function.

  10. Write the implementation for the getPick() function. Your getPick() function should only accept r, p, or s from the user. If they enter anything else, print an error message and ask again.

    r,p,s?: w
please enter r, p, or s!!!
r,p,s?: zebra
please enter r, p, or s!!!
r,p,s?: r

  11. Given the assignments for S, L, P, and C, what is the value and type of each expression?

s = "abcdefg"
L = ['Join me', 'and we can rule', 'the galaxy', 'as father and son']
P = Point(100,200)
C = Circle(P, 5)
                             VALUE            TYPE
                             -----            ----
len(L)
len(S)
len(L[1])
"a" in L[2]
"ABC" in S
L[0][0]
P.getX()
P.getX() > 600
C.getRadius()
C.getCenter().getY()