IT 117: Intermediate Scripting

IT 117: Intermediate to Scripting
Homework 4

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 29th 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.csv from /home/ghoffman/course_files/it117_files.
Use FileZilla to do this.

Specification

This script must read in a text file of cities and the states in which they are located

The file looks like this

New York City,New York
Los Angeles,California
Chicago,Illinois
...

It should use this file to create a dictionary ...
where the keys are state names ...
and the values are a list of cities in that state
It should then print states and their cities
And then print a list states and the number of cities they have
The script must have 4 functions:
- open_file_read
- cities_dictionary_create
- print_cities
- print_city_count

Functions

open_file_read

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

cities_dictionary_create

Header
```
def cities_dictionary_create(file)
```
The function must create a dictionary where the state is the key ...
and the value is a list of cites
The list of cities should be updated as new cities are read from the file

The function should use the following algorithm

create the empty dictionary cities
for each line in the file:
   get values for city and  state from the line
   if state not in cities
      create a new dictionary entry using state as the key  and  city as the value
   else
      get the cities_list of state from cities
      add city to cities_list 
      set the value for state to cities_list
return cities

print_cities

Header
```
def print_cities(dict):
```
This function must print the states and the cities they contain in alphabetical order by state
There should be one line for each city
The cities printed must be a string not a list
In other words, must turn the list of cities into a string and print that string

The function should use the following algorithm

for  in dict:
  set cities_string to the empty string
  set cities_list to the list of cities for state
  for city in cities_list:
    append city  and a space to cities_string
  print state and cities_string

print_city_count

Header
```
def print_city_count(dict):
```
The function must print the states and the number cities they contain in alphabetical order by state
There should be one line for each city

The function should use the following algorithm

for state in dict:
  print state and the length of the cities_list for state

Test Code

Your script must contain the following statements

file   = open_file_read("cities.csv")
cities = cities_dictionary_create(file)
if cities:
    print_cities(cities)
    print()
    print_city_count(cities)

They should appear at the bottom of your script
This code will only work if you have copied cities.csv 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

New York New York City 
California Los Angeles San Diego San Jose San Francisco Fresno Sacramento Long Beach Oakland 
Illinois Chicago 
Texas Houston San Antonio Dallas Austin Fort Worth El Paso Arlington 
Arizona Phoenix Tucson Mesa 
....

New York 1
California 8
Illinois 1
Texas 7
Arizona 3
...

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 hw4.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 hw3.py script.
Copy the test code into the bottom of the file.
Run the script.
Fix any errors you find.
Remove the pass statement from cities_dictionary_create.
Replace it with a statement that creates an empty dictionary named cities.
Write a for loop that loops through the file object file using line as the loop variable.
Inside the for loop use the strip method to remove the linefeed character from .
You will have to use an assignment statement to do this since strings are immutable.
Now print line.
Run the script.
Fix any errors you find.
Remove the print statement.
Now you are going to have to get the values for city and state.
You will do this using the split method on the string line.
Write an assignment statement that uses split to give values to the variables city and state .
For an example of what I mean, see Class Exercise 3.
You will have to give an argument to split.
Print city and state.
Run the script.
Fix any errors you find.
Remove the print statement.
Write an if statement that runs if state is not already in the cities dictionary.
You can use the in operator on cities to do this.
In the body of this if statement, create the empty list cities_list.
cities_list will contain the list of cities for each state.
Now write a statement that adds city to cities_list.
Outside the if statement, print the value of state and cities_list.
Run the script.
Fix any errors you find.
Remove the print statement.
Make an entry in the cities dictionary using state as the key and cities_list as the value.
Print state and the value associated with it in cities .
Run the script.
Fix any errors you find.
Remove the print statement.
The code you have written so far made an entry in cities each time an new value for state is read from the file.
Now we need to write code to add a new city to and existing entry for state.
You will do this with an else clause.
Inside this clause we need to get the current cities list associated with state and add the new value for city to this list.
Under else write an assignment state that gets the current value associated with state and assigns it to cities_list.
Write a statement to add city to cities_list using the append method.
Now update the value associated with state in the cities dictionary.
Print state and the value associated with it in cities .
Run the script.
Fix any errors you find.
Remove the print statement.
Outside the for loop write a statement to return the cities dictionary.
Remove the pass statement from print_cities.
Replace it with a statement that prints the value of its parameter dict.
Run the script.
You should see the entire cities dictionary.
Fix any errors you find.
Remove the print statement from print_cities.
Write a for loop, using state as the loop variable.
Inside the loop, print state and its value.
Run the script.
Fix any errors you find.
Remove the print statement.
Write an assignment statement that stores the value associated with state in the variable cities_list.
Print state and cities_list.
Run the script.
Fix any errors you find.
Remove the print statement.
Create the empty string cities_string.
Write a for loop over cities_list using city as the loop variable.
Inside the loop add each value of city to cities_string along with a space.
After the for loop print state and cities_string.
Run the script.
Fix any errors you find.
Remove the pass statement from print_city_count.
Print the parameter dict.
Run the script.
Fix any errors you find.
Remove the print statement.
Replace it with a for loop over the parameter dict using state as the loop variable.
Inside the for loop print state and the length of it's associated value.
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

New York New York City 
California Los Angeles San Diego San Jose San Francisco Fresno Sacramento Long Beach Oakland 
Illinois Chicago 
Texas Houston San Antonio Dallas Austin Fort Worth El Paso Arlington 
Arizona Phoenix Tucson Mesa 
....

New York 1
California 8
Illinois 1
Texas 7
Arizona 3
...

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.csv 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

New York New York City 
California Los Angeles San Diego San Jose San Francisco Fresno Sacramento Long Beach Oakland 
Illinois Chicago 
Texas Houston San Antonio Dallas Austin Fort Worth El Paso Arlington 
Arizona Phoenix Tucson Mesa 
....

New York 1
California 8
Illinois 1
Texas 7
Arizona 3
...