lab_debug

Learning Objectives

• Introduce and review common Python error messages
• Practice Python debugging skills
• Practice solving (and debugging) variable and conditional exercises

Submission Instructions

Using the Prairielearn workspace, test and save your solution to the following exercises. (You are welcome to download and work on the files locally but they must be re-uploaded or copied over to the workspace for submission).

Assignment Description

Understanding how to debug a program is – naturally – a very important skill for any coding work in your future. Unfortunately while we can discuss high level workflows or ‘tips and tricks’, the best way to learn this skill is through experiencing your own errors at your own pace. This lab is designed to artificially introduce many of the common mistakes you may encounter but truly learning to debug code will come over the entire semester’s workload.

For now, do your best to correct the accompanying short code snippets! You are strongly encouraged to work independently on this lab, but if you get stuck don’t hesistate to reach out to your peers or course staff! Likewise, if you are unclear about what a specific function should be doing, please reach out to course staff or your peers.

You may also find this Debug Guide (or the summary of it in the lab slides) helpful as a workflow. It will not solve your problems but may help you learn a systematic way of solving errors you encounter.

Part 1: Common Python Errors

The lecture portion of this lab will go over a number of common Python Error Messages you may encounter over the course of the class. You are encouraged to follow along with the starting Python notebook and complete the single debug problem at the end as proof of your work.

typeParser()

# INPUT:
# inVal, an arbitrary valued (and data typed) input
# OUTPUT:
# An integer with the following values:
# If the input is a string, return 1
# If the input is a float, return 2
# If the input is anything else, return 3
int typeParser(inVal):

Brad’s first attempt at writing a type parsing function is clearly incomplete but also contains several fundamental mistakes – some easier to spot than others! If you get stuck here are some hints to guide you along:

Hint: Your code should be able to handle any input (any type or value)! Is there a particular input type you are crashing on? Hint: The output of type() is not a string. What is it (or better yet – how could you create an object of the appropriate type to compare against?)

Part 2: Debugging Practice

Each of the following exercises is designed to test your knowledge of the Python fundamentals seen this week as well as your debugging skills. When completing these functions, you are strongly encouraged to debug the errors rather than immediately delete and rewrite the functions.

getGrade()

str getGrade(int score)
# INPUT:
# score is a number representing a student's score from 0 to 1000 (int)
# OUTPUT:
# A single character with the letter grade based on their score (str)
#
# Example: 
# getGrades(700) -> "C"
# getGrades(899) -> "B"

It’s the end of the semester and Brad has a problem – for some reason the grade breakdown he set up at the beginning of the semester just aren’t matching what his code is outputting. Can you figure out what Brad has done wrong and ensure that students get the grade they actually are supposed to?

The grade breakdown should match the syllabus for the class. That is to say:

NOTE: To make the intended boundaries more clear, each (non-F) letter grade should be assigned for scores starting at X00 and ending at X99 including those values. (For example, 799 is a C and 800 is a B). For more examples, see the workspace or autograder!

calculator()

# INPUT:
# a, a numeric input (float or int)
# b, a string input storing a number. You should assume its always a float
# c, a numeric input (float or int)
# OUTPUT:
# A string with precise formating for the value of '<a> + <b> + <c> = <sum>'
# <a>, <b>, <c>, and <sum> are all placeholders for the actual relevant values
# Each input as well as the sum should be rounded to two significant digits
string calculator(a, b, c):

Brad assumes that the reason why his ‘getGrades()’ function didnt work is because he doesnt actually know how to add numbers together properly. He tasks you with writing a Python script which will remind him of basic addition. Unfortunately he accidentally included a string as an input for variable b but can no longer change it as the input is now a permanent part of his workflow. Equally important, Brad’s grading system only works on up to two significant digits but the input could have many more digits than this!

Correct the code so that – even with a string input (guaranteed to store a number as a string) and two numeric inputs – Brad’s function will properly add the three inputs together.

Then make sure the output precisely matches the required output syntax:

1. Before any calculations, all inputs should be rounded to two significant digits and the output sum should also be rounded (if necessary).

2. The left side of the equals should list out the numeric value of each variable (a, b, c) with sums and spaces between them

3. The right side of the equals should be the actual numeric sum of the three inputs (dont forget the space after the equals!)

Some examples below Note the last one is an important edge case which will be tested!:

# Input: a = 3, b = "2.3", c = 2
'3 + 2.3 + 2 = 7.3'

# Input: a=-10, b = "5", c = 5
'-10 + 5.0 + 5 = 0'

# Input: a=3.33333, b = "5", c = -5
'3.33 + 5.0 - 5 = 3.33'

# Input: a=10.334, b = "0.3334", c = 15.334
'10.33 + 0.33 + 15.33 = 25.99'

intRemainder()

# INPUT:
# numer, an input number (float or int) storing the numerator of a fraction
# denom, an input number (float or int) storing the denominator of a fraction
# OUTPUT:
# The integer remainder of the fraction. 
# NOTE: You should conver the remainder into an integer, not the numerator or denominator
int intRemainder(numer, denom):

Brad’s next guess for why he can’t get student grades correct is that he’s accidentally been using integer division when getting individual assignment percentages! True to form for this particular assignment, rather than using regular division he’s invented a convoluted solution where he will just manually add back all the remainder points he’s been ignoring. For the sake of all students, please continue to fix Brad’s mistakes.

Some examples below:

# Input: numer = 1, denom = 1
0

# Input: numer = 13.5, denom = 5
3

validation()

# INPUT:
# inString, An input string of arbitrary size
# seq, An input string storing the validation sequence
# start, An input integer storing the start position of the validation sequence
# OUTPUT:
# A boolean (True or False) stating whether the input is valid or not
# A valid input is one where the full input sequence can be found starting at position start in the inString
# If the start position is invalid or out of bounds, you should return False
boolean validation(inString, seq, start):

Looking for a scapegoat for his failures, Brad naturally assumes that someone must have hacked his university account! However rather than change his password or double check his two-factor authentication, he has written his own password validation.

As it turns out, Brad’s solution works [for him] 100% of the time! But when he gave it to his friends, none of them could get it to work! As it turns out, Brad neglected to realize that people use passwords other than “AAA”! Help generalize the solution Brad has started so that it works for all possible inputs rather than a single hardcoded solution.

Some examples below:

# inString = "ABCDEFG", seq="CD", start = "2"
True

# inString = "ABCDEFG", seq="CD", start = "1"
False

# inString = "AAAAAAA", seq="AA", start = "1"
True

# inString = "AAAAAAA", seq="AAAAA", start = "5"
False

validShape()

# INPUT:
# sides, an integer storing the number of sides of a shape
# color, a string storing the color of an object
# xpos, an integer storing the x-position of a shape
# ypos, an integer storing the y-position of a shape
# OUTPUT:
# A boolean (True or False) stating whether the input shape is valid or not
# A valid shape must:
# - Have between 3-9 sides
# - Have a single character for a color from the following options: ('b', 'r', 'y', 'k')
# - Have positive valued xpos and ypos (consider 0 to be positive here)
boolean validShape(sides, color, xpos, ypos):

Brad’s first attempt at autograding the patches assignment validated the student shapes based on input arguments rather than pictures. However he couldnt get it to work right because he forgot how to use conditional expressions. Correct the following function to check that a student’s input shape matches the core requirements. That is to say:

1. The shape must have between 3 and 9 sides (including 3 and 9)
2. The shape must be colored blue, red, yellow, or black (‘b’, ‘r’, ‘y’, or ‘k’)
3. The shape must be in the positive x and positive y quadrant, where 0 is included as a positive value.

Some examples below:

# sides = 4, color="b", xpos = 1, ypos = 2
True

# sides = 10, color="b", xpos = 1, ypos = 2
False

# sides = 3, color="o", xpos = 1, ypos = 2
False

# sides = 8, color="r", xpos = -1, ypos = 2
False