IT 116: Intermediate Scripting

IT 116: Introduction to Scripting
Homework 8

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, November 2nd at 11:59 PM

What You Need to Do

Create the script hw8.py
Make sure it obeys the rules in Rules for Homework Scripts
Move it to an an hw8 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 hw8.py

Specification

This script will use functions in the random module create, read and work with files of integers
The script must contain 3 functions
- random_div_3
- random_file_create
- count_evens

Functions

random_div_3

Header
```
def random_div_3():
```
This function returns a random integer from 1 to 100 that is divisible by 3
The function should use the following algorithm

	while True:
	  get a random number
	  if the random number is divisible by 3:
	     return the number

random_file_create

Header
```
def random_file_create(file):
```
This function uses random_div_3 to create a file of 10 random integers divisible by 3

count_evens

Header
```
def count_evens(file):
```
This function returns the number of even integers in a file
The function should use the following algorithm

	set even_count to 0
	for each line:
	   convert line to number
	   if the number is even:
	      increment even_count
	return even_count

Test Code

Your script must contain the following statements

random.seed(67)
FILENAME = "numbers.txt"
file = open(FILENAME, "w")
random_file_create(file)
file = open(FILENAME, "r")
print(count_evens(file))

They should appear at the bottom of your script

Output

The output should look something like this
```
4
```

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

Copy only the function headers for the five functions listed above into your script file.
Under each header, write pass.
Make sure this statement is indented.
Run the script.
Fix any errors you find.
Remove the pass statement from random_file_create.
Replace it with a for loop that loops 10 times.
Inside the for loop print something.
Copy the test code to the bottom of your script.
Comment out all lines in the test script except the first four.
Run the script.
Fix any errors you find.
Remove the print statement from random_file_create.
Replace it with an assignment statement that give the variable number the value returned by calling random_div_3().
random_div_3 takes no argument.
Print number.
Remove the pass statement from random_div_3.
In its place write an assignment statement that gives the variable number a randomly chosen value between 1 and 100.
You can use random.randint() to create this value.
Return number.
Run the script.
Fix any errors you find.
Now you need to change the code so that random_div_3 only gives a value that is divisible by 3.
You will need a while loop to do this.
Remove the return statement.
Above the assignment statement for number write
```
while True:
```
This loop would normally run forever, but the code will break out of the loop using a return statement.
Under the assignment statement write an if statement that will work if number is divisible by 3.
You will need to use the remainder operator %.
A number is divisible by 3 if, when you divide the number by 3, the remainder is 0.
Inside the if statement return number.
Run the script.
Fix any errors you find.
Now you are need to change random_file_create so it writes number to the file pointed to by the file parameter.
This is a little bit complicated.
Instead of printing, you will have to make a call to file.write.
Since we need to create a text file, we will have to convert number to a string. Since each number must appear on a separate line, we must concatenate the linefeed character to the string version of number.
First remove the print statement in random_file_create.
Replace it with a call to file.write.
Inside the parentheses of the argument, convert number to a string and concatenate it with \n. Run the script.
To see if it worked look at the file Fix any errors you find.
Remove the pass statement from count_evens.
Give the variable even_count the value 0.
Loop through file with a for loop.
Inside the loop print each line.
Uncomment the last line in the test script.
Run the script.
You should see numbers with "None" on the last line.
Fix any errors you find.
Remove the print statement.
Replace it with an assignment statement that creates the variable number by converting each line into an integer.
Print number.
Run the script.
Fix any errors you find.
Remove the print statement.
Replace it with an if statement that will work if number is even.
You can do this using the remainder operator, %.
If a number is even, its remainder when divided by 2 is 0.
Inside the if statement increment even_count by 1.
Outside the for loop, return even_count.
Run the script.
Fix any errors you find.

Testing on Your Machine

Open IDLE
Use the Open command in IDLE to open hw8.py
Run your script inside IDLE
Your output should look something like this
```
4
```

Copy the Script to Unix

Open FileZilla and connect to pe15.cs.umb.edu
Go to your it116 directory
Go to your hw directory
Right-click in the whitespace inside the hw directory
Enter hw8 in the dialog box
Click and drag your script 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  it116/hw/hw8
```
Run this script
```
python3 hw8.py
```
You should see something like this
```
4
```
The text in blue is what you enter at the command line