IT 117: Intermediate Scripting

IT 117: Introduction to Scripting
Homework 6

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, March 8th at 11:59 PM

What You Need to Do

Create the script hw6.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 hw6 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 hw6.py
Copy the directory hw6_test_dir from /home/ghoffman/course_files/it117_files.
Use FileZilla to do this.

Specification

This script will contain functions that use the os and sys modules
Though the script is designed to run on pe15.cs.umb.edu it can be run on your machine with a few adjustments
The script must contain 3 functions
- get_command_line_arguments
- print_path_dirs
- python_file_count

Functions

get_command_line_arguments

Header

def get_command_line_arguments(arg_number):

This function looks at the command line arguments.
The number of command line arguments returned is specified by the parameter arg_number
If the user does not enter the proper number of the command line arguments, the function should print a usage message and exit the script
This message must have the following format where 6 is the number of command line arguments specified by the parameter arg_number
```
 
Usage: SCRIPT_NAME requires 6 arguments
```
If the number of command line arguments is greater than or equal to the number of command line arguments, it should return a string with just the number of argument given by the parameter arg_number

print_path_dirs

Header
```
def print_path_dirs():
```
This function must print the directories listed in the PATH system variable
Each directory must be on a separate line

python_file_count

Header
```
def python_file_count(dir):
```
This function must count the number of files with a .py extension in the directory specified by dir
It should return this number

Test Code

Your script must contain the following statements

get_command_line_arguments(2)
args = get_command_line_arguments(2)
print(args)
print()
print_path_dirs()
print()
dir = "hw6_test_dir"
py_count = python_file_count(dir)
print("Python files: ", py_count)

They should appear at the bottom of your script
This code will only work if you have copied the directory hw6_test_dir 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

['foo', 'bar']

/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/sbin
/bin
/usr/games
/usr/local/games
...

Python files:  3

The directory listing you see may be different depending on which machine you run the script

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 hw6.py.
Import the os and sys modules.
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.
Remove the pass statement from get_command_line_arguments.
Print the value of sys.argv.
Copy the test code to the bottom of the script.
Comment out all but the first line of the code.
Run the script with 0, 1 and 2 command line arguments.
Fix any errors you find.
Remove the print statement.
Add an if statement that will execute if the user has entered fewer than the number of arguments specified by the parameter arg_number.
Remember that the first entry in the list of things on the command line is the name of the script.
So the length of the list of command line entries is NOT the number command line arguments.
The body of this if statement should print "ERROR".
Under the print statement write a statement that quits the script.
Run the script with 0, 1 and 2 command line arguments.
Fix any errors you find.
Replace the error message with the usage message given above.
Remember I want the name of the script not the pathname used to run it.
You will need to use the first element in sys.argv and os.path.basename.
See Usage Messages .
Run the script with 0, 1 and 2 command line arguments.
Fix any errors you find.
Outside the if statement create the empty list values.
You need to fill this list with the command line arguments.
You can do this with a for loop that uses the range function to create indexes from 1 to the length of arg_number .
Inside the loop use the index to get the value of the command line argument, then append it to values.
Uncomment the next two lines in the test code.
Run the script with 2 command line arguments.
You should see the script print these two arguments.
Fix any errors you find.
Remove the pass statement from print_path_dirs.
Write an assignment statement that gives the variable path the value of the system variable PATH.
To get this value you will need to use a variable in the os module that is a dictionary where system variable names are the keys and the values are the value of each system variable.
Print path. Uncomment the next two lines in the test code.
Run the script with 2 command line arguments.
Fix any errors you find.
Remove the print statement.
The PATH system variable contains the absolute pathnames of directories holding executable files.
Each of these pathnames is separated from the next with a :.
On a Windows machine the character is ;
Create the list dirs by running the string split method on path.
Print this list.
Run the script with 2 command line arguments.
Fix any errors you find.
Remove the print statement.
Replace it with a for loop that prints each directory in dirs.
Run the script with 2 command line arguments.
You should see a list of directories on your machine.
Fix any errors you find.
Remove the pass statement from python_file_count.
Add a statement that will change directory to the pathname contained the dir parameter.
Create the list entries using a function in the os module that returns a list of everything inside a directory.
Print this list.
Uncomment the next three lines in the test code.
Run the script.
Fix any errors you find.
Remove the print statement.
Create the variable count and set it to 0.
Write a for loop that iterates over entries.
Inside the for loop write an if statement that print an entry if it is a file.
There is a function in os.path that returns True if its argument is a file.
Run the script.
Fix any errors you find.
Remove the print statement. Replace it with an if statement that looks for files whose name ends in ".py".
Use the string method endswith to do this. In the body of this if statement write a statement which increments count by 1.
Outside the for loop return the value of count.
Uncomment the last line of the test code.
Run the script with 2 command line arguments.
The number of ".py" files should be 3. Fix any errors you find.

Testing on Your Machine

Open IDLE
Use the Open command in IDLE to open hw6.py
If you have a windows machine change : to ; in the argument to split()
Under the Run menu, select Run Module
This script needs command line arguments
Under the Run menu select Run ... Customized
Enter two command line arguments

Your output should look something like this

['foo', 'bar']

/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/sbin
/bin
/usr/games
/usr/local/games
...

Python files:  3

The directory listing you see may be different depending on which machine you run the script

Copy the Script to Unix

If you have changed the argument to spit() from : to ;, change it back to :
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 hw6 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 the directory hw6_test_dir 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/hw6
```
Run this script
```
hw6.py foo bar
```

You should see something like this

['foo', 'bar']

/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/sbin
/bin
/usr/games
/usr/local/games
...

Python files:  3

The directory listing you see may be different depending on which machine you run the script