IT 117: Intermediate Scripting

IT 117: Introduction to Scripting
Homework 3

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, February 15th at 11:59 PM

What You Need to Do

Create the script hw3.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 hw3 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 hw3.py
Copy the file state_populations.txt from /home/ghoffman/course_files/it117_files.
Use FileZilla to do this.

Specification

This script will read in a text file containing a list of states and their populations

The file has entries like the following

California,39512223
Texas,28995881
Florida,21477737
New York,19453561
...

The script should create a dictionary where the keys are the state names and the values are the population
It should then print the dictionary in alphabetical order
The script must contain 3 functions
- open_file_read
- state_dictionary_create
- print_dictionary

Functions

open_file_read

Header
```
def open_file_read(filename):
```
The function must create a file object for reading on the file whose name is given by the parameter filename
If it can create the object it should return it
If it is cannot create the object it should print an error message and return None

state_dictionary_create

Header
```
def state_dictionary_create(file):
```
This function has one parameter, file, a file object for reading
It should loop through the file obtaining values for the state name and population
It should use these values to create entries in a dictionary where state names are the key and populations are the value
The population must be stored as an integer
The function should return the dictionary it creates
The function should use the following algorithm

	create an empty dictionary
	for each line in the file
		get values for state name and population
		convert population into an integer
		create a dictionary entry with the state name as the key and population the value
	return the dictionary

print_dictionary

Header
```
def print_dictionary(dict):
```
This function has one parameter, dict, a dictionary
The function must print the key and value for each entry in the dictionary, sorted by key

Test Code

Your script must contain the following statements

filename = input("File name: ")
file = open_file_read(filename)
if file:
    state_populations = state_dictionary_create(file)
    if state_populations:
        print_dictionary(state_populations)

They should appear at the bottom of your script
This code will only work if you have copied state_populations.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: state_populations.txt
Alabama 4903185
Alaska 731545
Arizona 7278717
...

The text in blue is what the user enters

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

Create the file hw3.py.
Enter the headers for each of the required functions.
Under each header write the Python statement pass.
Run the script.
Fix any errors you find.
Replace the pass statement in open_file_read with the body of the code from your hw2.py script.
Copy the test code into the bottom of the file.
Comment out all but the first two lines.
Run the script entering both a real filename and the name of a file that does not exists.
Fix any errors you find.
Replace the pass statement in state_dictionary_create with a statement that creates the empty dictionary state_pop.
Write a for loop that prints each line in the file.
Uncomment the next two lines in the test code.
Run the script entering state_populations.txt when prompted.
Fix any errors you find.
Remove the print statement.
Create the list variable fields by calling the split method on each line.
Use fields to get the values for the variables state and population.
If you are not sure what I mean, see Class Exercise 2.
Use an assignment statement to convert population into an integer.
Print the values of state and population.
Run the script.
Fix any errors you find.
Remove the print statement.
Inside the for loop create an entry in the dictionary using state as the key and population as the value.
After the for loop return the dictionary.
Run the script.
Fix any errors you find.
Remove the pass statement from print_dictionary.
Replace it with a line that prints the value of the parameter, dict.
Uncomment the last two lines of the test code.
Run the script.
Fix any errors you find.
Remove the print statement,
Replace it with a for loop that prints the key and value for each entry in the dictionary.
Remember the entries must be sorted by state.
Run the script.
Fix any errors you find.

Testing on Your Machine

Open IDLE
Use the Open command in IDLE to open hw3.py
Under the Run menu, select Run Module

Your output should look something like this

File name: state_populations.txt
Alabama 4903185
Alaska 731545
Arizona 7278717
...

The text in blue is what the user enters

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 hw3 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 state_populations.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/hw3
```
Run this script
```
hw3.py
```

You should see something like this

File name: state_populations.txt
Alabama 4903185
Alaska 731545
Arizona 7278717
...