• Due
• What You Need to Do
• Setup On Your Machine
• Specification
• Functions
• Test Code
• Output
• Suggestions
• Testing on Your Machine
• Copy the Script to Unix
• Testing the Script on Unix (Optional)

Due

Sunday, September 28th at 11:59 PM

What You Need to Do

• Create the script hw4.py
• Make sure it obeys the rules in Rules for Homework Scripts
• Make sure the script has a hashbang line and is executable
• Move it to an an hw4 directory on pe15.cs.umb.edu

Setup On Your Machine

• Open a text editor.
  I would suggest the text editor built into the program IDLE.
• Save the file as hw4.py
• Copy the file cities_counties_cases.txt from /home/ghoffman/course_files/it117_files.
  Use FileZilla to do this.

Specification

• This script reads file with 3 values
  • city
  • County
  • Number of cases
  on each line
• The file looks like this

  Barnstable,Barnstable,1
  Bourne,Barnstable,5
  Brewster,Barnstable,9
  ...

• It should create a dictionary where the county is the key and the total number of cases for the country is the value
• The script must contain 3 functions
  • open_file_read
  • cases_dictionary_create
  • highest_cases
• The script should print the name of the county with the highest number of cases along with the total cases

Functions

open_file_read

• Header

  def open_file_read(filename):

• The script must try to create a file object for reading on the file whose name is given by the parameter filename
• If it is succesful it should return the file object
• Otherwise it should print an error message and return None

cases_dictionary_create

• Header

  def cases_dictionary_create(file):

• This function uses the file object given by the parameter file to read a file line by line
• It uses the data in the line to create a dictionary
• Where counties are the key and the vales is the total number of cases for that county
• The function should return this dictionary

highest_cases

• Header

  def highest_cases(county_cases):

• The function should loop through the dictionary given by the parameter county_cases
• It should find the county with the highest number of cases
• And return that county and the numer of cases

Test Code

• Your script must contain the following statements
• They should appear at the bottom of your script

filename = input("File name: ")
file = open_file_read(filename)
if file:
	cases = cases_dictionary_create(file)
	max_county, max_cases = highest_cases(cases)
	print(max_county,max_cases)

• This code will only work if you have copied cities_counties_cases.txt into the same directory as your script
• You will find this file in /home/ghoffman/course_files/it117_files

Output

• The output should look something like this

  File name: cities_counties_cases.txt
  Worcester 455

Suggestions

• Write this script in stages
• Test your script at each step
• Print the steps below
• And check them off as you finish each one

1. Create the file hw4.py.
   Enter the headers for open_file_read, cases_dictionary_create and highest_cases.
   Under each header write the Python statement pass.
   Run the script.
   Fix any errors you find.
2. Replace the pass statement in open_file_read with the body of the code from your hw2.py.
   Copy the test code to the bottom of the file.
   We want the first two lines to run now.
   To make this happen, we need to comment out all but the first two lines of the test code.
   Run the script entering both a real filename and the name of a file that does not exists.
   Fix any errors you find.
3. Remove the pass statement from cases_dictionary_create.
   Create the empty dictionary county_cases.
   Write a for loop that prints every line in the file.
   Uncomment the next two lines of the test code.
   Run the script entering cities_counties_cases.txt when prompted.
   Fix any errors you find.
4. Remove the print statement.
   Use the split string method on each line in the file to assign values to the variables city, county and cases.
   You will have to give split the argument "," since a comma appears between each value on the line.
   Use either one of the techniques found in Class Exercise 2 or Class Exercise 3 to assign values to the variables.
   Write and assignment statement that converts cases to an integer.
   Print the value of the three variables.
   Run the script.
   Fix any errors you find.
5. Remove the print statement.
   When the script comes across a value for count that it has not seen before, it needs to create an entry for this new key.
   That entry will be the number contained in cases.
   Write an if statement that checks whether the the value of county is already in county_cases.
   If it is, create a new entry in county_cases with county as the key and cases as the value.
   Outside the for loop print the dictionary county_cases.
   Run the script.
   Fix any errors you find.
6. Now we have to deal with the situation where the value for county is already in the dictionary.
   In cases_dictionary_create, continue the if statement with an else clause.
   In the code block for this new clause, get the current value for cases associated with the county and assign it to the variable current_casses.
   Under this write a statement that sets the new value in the dictionary for country to be the sum of cases and current cases.
   Run the script.
   Fix any errors you find.
7. We need to finish the work on cases_dictionary_create so we can proceed to highest_cases.
   All we have to do here is replace the print statement with a statement that returns the dictionary county_cases.
   Now go to highest_cases and remove the pass statement.
   In it's place write a for loop that loops through the entries in the dictionary.
   Inside the loop print the key and value for each entry.
   Run the script.
   Fix any errors you find.
8. Now you are going to have to find the county with the highest number of cases.
   You should use the same technique used in Class Exercise 3.
   Above the for loop assign the variable max_cases the value 0 and assign max_county the empty string.
   Remove the print statement inside the for loop.
   Write and if statement that checks whether the value of cases is greater than max_cases.
   If it is, set max_caes to the value of cases and max_county to county.
   Outside the for loop return max_county and max_cases.
   Uncomment the last line of the test code.
   Run the script.
   Fix any errors you find.

Testing on Your Machine

• Open IDLE
• Use the Open command in IDLE to open hw4.py
• Under the Run menu, select Run Module
• Your output should look something like this

  File name: cities_counties_cases.txt
  Worcester 455

Copy the Script to Unix

• Open FileZilla and connect to pe15.cs.umb.edu
• Go to your it117 directory
• Go to your hw directory
• Right-click in the whitespace inside the hw directory
• Enter hw4 in the dialog box
• Click and drag your script from the bottom left panel to the bottom right panel
• Right-click on the file and select "Permissions" from the menu
• Enter 755 in the box provided
• This will make the script executable
• Click and drag cities_counties_cases.txt from the bottom left panel to the bottom right panel

Testing the Script on Unix (Optional)

• Connect to pe15.cs.umb.edu using an ssh client like putty.exe (Windows) or ssh (Mac)
• Go to the directory for this exercise

  cd  it117/hw/hw4

• Run this script

  hw4.py

• You should see something like this

  $ ./hw4.py 
  File name: cities_counties_cases.txt
  Worcester 455

Copyright © 2020 Glenn Hoffman. All rights reserved. May not be reproduced without permission.