CMU 15-112 Spring 2019: Fundamentals of Programming and Computer Science
Lab 3 (Due as part of hw3 on Sunday 3-Feb, at 5pm)

• Reminder: Lab problems must be solved collaboratively with at least one other student. List your collaborators!
• Do not complete these problems before your scheduled lab on Friday; we'll just make you work on them again with another student, or you won't get the lab attendance credit.


• You should put the solutions to these problems in your hw3.py file. Follow these steps if you haven't started yet!:
  1. Create a folder named 'week3'
  2. Download both hw3.py and cs112_s19_week3_linter.py and hw3_files.zip to that folder. Unzip hw3_files.zip in the folder.
  3. Edit hw3.py using Pyzo
• Do not use lists, list indexing, sets, dictionaries, or recursion this week.
• Do not hardcode the test cases in your solutions.
• Your hw3 file should contain answers to these problems (25pts) plus the hw3 problems released earlier this week (75pts)

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Collaborative lab problems

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1. COLLABORATIVE Code Writing: gradebookSummary(gradebookFilename) [15 pts]
   For this problem, we'll assume that gradebooks are stored in .txt files. Each row of the gradebook file contains a student's name (one word, all lowercase), followed by one or more comma-separated integer grades. A gradebook always contains at least one student, and each row always contains at least one grade. Gradebooks can also contain blank lines and lines starting with the "#" character, which should be ignored.
   
   With this in mind, write the function gradebookSummary(gradebookFilename) that takes the filename of a gradebook as an argument and returns a summary of the gradebook as a string. This summary string should show each student followed by a tab followed by their average grade (rounded to the hundreth place). The summary string should have the students listed in their original order (separated by newlines, but without a newline at the end), but should get rid of any comments or blank lines.
   
   For example, here is a test case:
   
   
   # the following string is the content of the file gradebook1.txt """# ignore blank lines and lines starting with #'s wilma,91,93,94 fred,80,85,90,97,100 betty,88""" assert(gradebookSummary("gradebook1.txt") == "wilma\t92.67\nfred\t90.40\nbetty\t88.00"))
   
   Hint: You may wonder how to locate and distinguish the name on each gradebook line from the scores... one approach would be to look for the first comma after a newline.
   (Note: If you think you know an easy way to solve this problem but the linter bans your solution, it's probably because you're using a concept we haven't taught yet!)


2. COLLABORATIVE Code Writing: applyCaesarCipher(message, shiftNum) [10 pts]
   A Caesar Cipher is a simple cipher that works by shifting each letter in the given message by a certain number. For example, if we shift the message "We Attack At Dawn" by 1 letter, it becomes "Xf Buubdl Bu Ebxo".
   
   Write the function applyCaesarCipher(message, shiftNum) which shifts the given message by shiftNum letters. You are guaranteed that message is a string, and that shiftNum is an integer between -25 and 25. Capital letters should stay capital and lowercase letters should stay lowercase, and non-letter characters should not be changed. Note that "Z" wraps around to "A". So, for example:
   
   
   assert(applyCaesarCipher("We Attack At Dawn", 1) == "Xf Buubdl Bu Ebxo") assert(applyCaesarCipher("zodiac", -2) == "xmbgya")

If you finish early, consider working on the collaborative problem mostFrequentLetters from hw3.