Lab 8: Practice with Modules and Files

Objective: Review

Review the slides for today's lab.

Objective: Set Up

• Set up the help client:

  run runHelpClient &

• Copy /csdept/courses/cs111/handouts/lab8 and all of its contents, recursively, into your cs111 directory. This way, you don't have to create the lab8 directory first. Otherwise, you could first create the lab8 directory and then copy all of the contents of the /csdept/courses/cs111/handouts/lab8 directory (i.e., add a * to the cp command) into your lab8 directory.

Objective: Programming in Python

1. (15) Creating a module. Modules are a way that we can make our code easier to reuse and share. We've used modules but haven't made our own modules explicitly. That changes now.

   Copy (one of your) lab7.8.py and name it caesarcipher.py. Create a new file called lab8.1.py. Move the main function and calling the main function from caesarcipher.py into lab8.1.py.

   Confirm: caesarcipher.py should contain only the definitions of the encoding functions and the test functions, comments at the top that describe the module, and maybe constants.

   Near the top of lab8.1.py, import your module by adding an import statement: from caesarcipher import *

   Run lab8.1.py to confirm that it still works as expected.

   Next, modify caesarcipher.py to call your test functions at the bottom of the file. Run lab8.1.py. What happened?

   To handle that issue, we need to add some code into caesarcipher.py: put the calls to the test functions into the body of an if statement, specifically: if __name__ == "__main__":

   Run caesarcipher.py. What happens?

   Run lab8.1.py. What happened?

   Reflection: Explain in comments in caesarcipher.py what the effect of adding that if statement was, on both caesarcipher.py and lab8.1.py.

   For your .out file, demonstrate that lab8.1.py works as expected.

2. (20) Modify caesarcipher.py such that it encodes many phrases using the Caesar Cipher program. Specifically, you will add a function called encodeFile that takes as parameters a filename (as a str) and a key and returns the whole file encoded, as a string, preserving new line characters.

   Write a function to test this function. For example, process the data/phrases.txt file that you copied from the handouts directory. Better than starting with data/phrases.txt, you should create your own (simpler) files to test the encoding. What would be good, smaller files that would help show that your code works?

   Note: We're keeping the data files in a separate directory from the Python programs, which is good practice.

   Copy lab8.1.py into lab8.2.py. Then, modify its main function such that it prompts the user for (1) the name of a file that contains phrases that need to be encoded and (2) a key, reads the file of phrases to be encoded, and outputs the encoded phrase.

   Example final output:

   This program will encode a whole file using Caesar ciphers.
   
   Enter the name of a file to encode: data/song.txt
   Enter an encoder key (an integer between -25 and 25): 1
   The encoded file is
   uijt pof hpft pvu up uif pof j mpwf
   uijt pof hpft pvu up uif pof j mfgu cfijoe
   

   Doesn't that make testing the encodings a little easier, since you don't need to type out the whole phrase every time you test?

3. (15) Update caesarcipher.py so that it has a function called writeEncodedFile that takes as parameters the encoded message and the name of the file to write to, both as strings. Note that we can't write use test.testEqual to test the writing of a file. How can you test that your program works?

   Copy lab8.2.py as lab8.3.py and modify the main function such that it also takes as input the encoded message output file's name. You may want to assume that the output files always get written to the data directory so that you don't clutter your lab8 directory with files.

   The idea is that now you can encode files that you can give to others to decode (and vice versa).

   Example output:

   What is the name of your file to encode? phrases.txt
   What is the name of the file to output the encoded file to? encoded.txt
   What is the key to use to encode? 12
   Your message has been successfully written to data/encoded.txt
   

   Note: I broke up the large problem of encoding files using a Caesar cipher and writing the result into another file into multiple, smaller problems, each of which is easier to tackle than tackling the whole problem all at once. This is an important problem-solving skill to develop. You may feel like breaking the problem into smaller problems slows you down, but it usually doesn't because you spend less time debugging the smaller pieces than if you had tackled it all at once. You'll get lots of practice solving problems in this class--including on the next problems!

4. (15) Modify caesarcipher.py to do exception handling when reading the file and when writing to the file. When a problem with reading or writing a file occurs, display a descriptive error message and then exit the program. To exit the program, you'll need to import sys at the top of the program and then call sys.exit(). Update the doc strings for the functions accordingly.

   Demonstrate that the program works as expected on files that exist and displays an error message on files that don't. For writing files, try writing to a location that you don't have permission to write to, e.g., /etc/myfile.txt Note that we can't set up our test functions to be able to check that the exception behavior works because of how we have our functions set up.

   Save this output in lab8.4.out.

5. (35) The system of scoring an Olympic gymnast is based on two separate panels of scores. The A panel judges the requirements, difficulty, and connections of a routine. The scoring starts at zero and then adds points accordingly. The B panel judges the execution of a routine, and the scoring starts at 10 with points deducted accordingly for execution and for any applicable violations such as stepping out of bounds or being over the time limit.

   For each panel of judges, the lowest and highest scores are dropped (to prevent judges from biasing the results) and then averaged. The two panels are then added together for the final score. A very good score will range in the 15s and 16s.

   Your task:

   1. Read in a file containing the gymnastics scores. (The file name can be a constant in your program.) The first line of the file is the already-averaged difficulty score. The remaining six lines are the judges' execution scores. (You cannot assume that the execution scores are sorted.)

      Example input file:

      5.7
      8.3
      9.1
      8.0
      8.9
      8.8
      8.5
      

   2. Calculate the average score for the execution scores, as described above.
   3. Display the judges' scores and the final score in the format shown below.

      Example output:

      Gymnastics Scores for data/scores.dat
      --------------------------------------------------------
              Judges Execution Scores: 8.0 8.3 8.5 8.8 8.9 9.1 
              Average Execution Score: 8.625
              Average Difficulty Score: 5.7
              The Final Score: 14.325
      

      Your output does not need to display the scores in sorted order. However, the output should be formatted as above.

      Example files are data/nastia.dat and data/shawn.dat

   Breaking Down the Problem: Your final program should have at least 3 functions:

   • A function that takes as a parameter the name of the file and returns a list of the scores (as floats) that are in the file.
   • A function that takes as a parameter the list of scores (as floats) and returns the "unbiased" average.
   • A main function

Finishing up: What to turn in for this lab

1. When you, as a pair, are ready to submit OR if you are at the end of the lab period, run pairturnin.sh labx partnerusername
   where labx is the name of the lab you are submitting and partnerusername is your partner's username on the lab machines (the person whose account you are not using to write the code). For more information about the command, see the wiki.

   If you want to copy your pairs' work into your cs111 directory--either just to have it or to work on your code on your own--use the script startup.sh. Run this command from the account that you want For example, run startup.sh labx partnerusername
   where labx is the name of the lab you're working on and partnerusername is your partner's username on the lab machines.

   For more info, see the wiki.

2. If you complete the lab on your own after the lab period, submit your lab into your turnin directory.

Perform the following steps from your cs111 directory.

Note that each command below links to a page with more information about using the command.

3. Create the printable lab assignment, using the createPrintableLab command:
   createPrintableLab <labdirname>
4. View your file using the evince command.
5. Print the file using the lpr command.
6. Log out of your machine when you are done.

Labs are due at the beginning of Friday's class. You should hand in the printed copy at the beginning of class, and the electronic version should be in the turnin directory before Friday.

Ask well before the deadline if you need help turning in your assignment!

Grading (100 pts)

• Python programs: 100 pts; see above for breakdown