IT 116: Introduction to Scripting

IT 116: Introduction to Scripting
Class 2

Course Work

Assignments
Submitting Assignments
Working on Assignments
Software for the Class
Class Assistant

New Material

Files
Directories (Folders)
Working With Files
Your Unix Course Directory
Types of Programming Languages
Python
Downloading Python
Running IDLE
Syntax Highlighting
Creating a Python Script
Running a Script in IDLE
Changing a Python Script
Two Ways to Run Python
Python in Class Exercises
Running Python in Interactive Mode
Python on Unix
Scripts versus Interactive Mode
Using FileZilla
Today's Class Exercise

Microphone

Readings

If you have the textbook you should read Chapter 1, Introduction to Computers and Programming, from the textbook, Starting Out with Python.

Homework 1

Remember, homework 1 is due this Sunday by 11:59 PM.

You will find it here.

Unix Account and Class Directory

Some you have not created a class directory and a Unix account.

All work for this course MUST be copied to your class directory

A directory is what you probably call a "folder".

Without a class directory you cannot submit assignments.

If you do not have a Unix account go to http://www.cs.umb.edu/~ghoffman/linux/cs_portal.html#creating_unix_account.

If you do have a Unix account you still need a class directory for this course.

Go to https://portal.cs.umb.edu/accounts/login/ , log in, click the check box for my section of this course, and click submit.

Help with Creating a Unix Account

If you have difficulty creating an account must get help NOW!

You can see me after class or during office hours.

You can contact me on Zoom during office hours.

To see how to do this go here

Or you can contact the Class Assistant.

Whatever it takes, you MUST create a Unix account and a class directory.

Questions

Are there any questions before I begin?

Course Work

Assignments

There are two types of assignments for this course
- Class Exercises
- Homework assignments
In the Class Exercise you simply copy some code
The idea is to give you some practice writing and debugging Python code
For homework assignments you write your own code
There is a Class Exercise for each class
There is one homework assignment each week
All Class Exercises and homework assignments are due on the Sunday after they are assigned
If you miss the deadline you can still submit your scripts until the following Saturday
But you will lose 2 points for each day you are late

Submitting Assignments

You can create the scripts for assignments on your machine
But they must copied to your class directory on pe15.cs.umb.edu
I will only score assignments copied to your class directory on pe15.cs.umb.edu
You will find a link to your class directory in your Unix home directory
When you first connect to a Unix machine you will be in your home directory
In todays Class Exercise you will create two directories in your class directory
- An hw directory for homework assignments
- An ex directory for Class Exercises
You must create a new directory under hw for each homework assignment
And you must create a new directory under ex or each Class Exercise
If a file is in the wrong directory or has the wrong name you will get a 0 for the assignment

Working on Assignments

Work on class assignments has two phases
In the first phase you will write, test and debug the script on your machine
In the second phase you will move the script to pe15.cs.umb.edu
You should also run your script on the Unix machine to make sure it works

Software for the Class

You need different software for each phase
For the first phase you need to download Python
You find instructions here
Python comes with a program called IDLE
You can use IDLE to run Python statements and create scripts
For the second phase you need
- An SSH client
- FileZilla
The SSH client allows you to log in to a Unix machine from your computer
You will need it to test the assignments to make sure they run correctly
If you have a Windows machine see Connecting to a Unix machine from Windows
If you have a Mac see Connecting to a Unix machine from MacOS
You will need FileZilla to copy your script to your class directory
You will find instructions here

Class Assistant

Imran Rashid is an undergraduate IT student who can help you with your assignments
You can reach him at Imran.Rashid001@umb.edu.
You should contact the Class Assistant if you are having trouble submitting your assignments
I have asked the Class Assistant to schedule a Zoom seesion each weekend to help you with any issues you might have
You will find the details here

New Material

Files

In order to do anything in this course you have to know about about files
A file contains data and is linear
That means it has a beginning and and end
Like a piece of string
Files exist on hardware like hard disks, SSDs and thumb drives
These devices are called long term storage
They store the files you create ...
so you can use them later
Any file you create on such devices will not disappear ...
unless you delete it
You create a file whenever you take a picture, save a Word document or send an email
All the information that computers use is contained in files
The programs you write for this course will be stored in files

Directories (Folders)

The hard drive on your computer probably has hundreds of files
The Unix machine we will be using for this course has even more
It is very important that files are well organized ...
or you will not be able to use the data that you create
To organize your files you need to create directories
Which are also called folders
The purpose of a directory is to hold files
And other directories
There is one special directory at the top
On Unix machines this is called the root directory
Every file on the machine is contained in this top directory ...
or a subdirectory of the top directory ...
or a sub-subdirectory
And so on
You can create as many directories as you want
If you drew a map of all the directories on a machine
It would look like a pyramid

Working With Files

You will create a file containing Python code for each assignment
Both Class Exercises and homework assignments
You will create these files on your machine
But you must remember where you put them
If you are careless and forget where you put a file ...
or put it in the wrong place ...
all your hard work will be lost until you find it
Files never disappear
Unless you delete them
If you can't find a file you created it isn't gone
It's just in the wrong place
Most computers these days have a Documents directory
You should create a python directory inside Documents
And save all your Python files there
When your code runs properly you need to copy them to pe15 ...
which is a Unix machine on the CS network
You will do this using a program called FileZilla
But you must put them in the right directory on pe15 ...
or I will not be able to find them

Your Unix Course Directory

You create your Python files on your machine
But I can't see them there
So you need to move them to the Unix machine pe15 ...
where I can see them
But you need to put them in a particular directory ...
or I won't know where to look
There is a special directory on pe15 for this class
Once you register for this class on the CS Portal you will have your own directory ...
inside this class directory
The directory name will be your Unix account name
My Unix account is ghoffman
I registered for this class on the CS Portal
So I have a ghoffman directory in the class directory

Types of Programming Languages

There are two broad classes of programming languages:
- Compiled languages
- Scripting languages
Compiled languages, like C, C++ and Java are used in large programming projects
In a compiled language, you create a text file consisting of instructions in the language
This file is called the source code
A source code file is written by programmers in a computer language
But it cannot, by itself, be run on a computer
In order to run the program you must create an executable file
This file contains the binary instructions that the CPU understands
For example, here is the source code for a simple program written in C:
```
#include <stdio.h>

main()
{
    printf("Hello, world!\n");
}
```
To create an executable file I must run the source code through a program called a C compiler
```
$ gcc -o hello hello.c
```
This program creates the executable file hello, which I can run on the Unix machine
```
$ ./hello 
Hello, world!
```
Compiled languages are designed for big programming projects
They are overkill for simple system administration tasks
Let's say you wanted to remove all files in a directory that have the .tmp extension ...
and were created before a certain date
You would not want to write a C program to do this
C is very finicky about syntax
You would probably see a lot of compile errors before you got a working program in C
Scripting languages were created to write small programs for tasks like this
Programs written in a scripting languages are not compiled
Instead they are run using an interpreter
An interpreter is a program that understands the scripting language
The interpreter reads the Python statements ...
turns them into the binary language the CPU understands ...
and the runs those binary instructions
There are a number of scripting languages commonly in use today
- Perl
- PHP
- Python
- Ruby
We will be learning Python

Python

Python was conceived in the late 1980s
It was first implemented in December 1989 by Guido van Rossum in the Netherlands
There are two versions of Python currently in use
- Python 2
- Python 3
Python 2 was released in October 2000
Python 3 is the latest version of Python
Unfortunately, scripts written in Python 3 will not always work in Python 2
And vice versa
We will be using Python 3 in this course
The Python design philosophy emphasizes code readability
It tries to express concepts in fewer lines of code than languages such as C
The core philosophy of Python is spelled out in the document "PEP 20 (The Zen of Python)"
It includes the following statements
- Beautiful is better than ugly
- Explicit is better than implicit
- Simple is better than complex
- Complex is better than complicated
- Readability counts

Downloading Python

Go to https://www.python.org/downloads/ and download the latest version of Python
The version number should be greater than 3.5
This will create a Python directory on your machine
Inside this directory you will find an application named IDLE

Running IDLE

Open IDLE
You will see a window like this

You are now running the Python interpreter
The three > signs, >>>, are a prompt
It is the interpreter's way of saying it is ready for you ...
to type a Python statement
Let's write a Python statement that will print a simple message

When you hit Enter or Return
The interpreter will run the statement

It has printed the text inside the parentheses ...
and issued a new prompt ...
to say it is ready for your next statement
When you run IDLE you are talking directly to the Python interpreter
This is called running Python in interactive mode

Syntax Highlighting

Notice that different parts of the window text appear in different colors
print appears in purple
That means print is function
The "Hello world!" inside the parenthesis appears in green
It is a string of characters
The output of the print statement appears in blue
Different words mean different things
And they appear in different colors
This is called syntax highlighting
It is a feature you will find in most text editors used by programmers
Syntax highlighting can make it easier to find mistakes in your code

Creating a Python Script

If you click and drag down to to "New File" you will get a new window

Notice that there is no >>> prompt in this window
That's because you are not running the Python interpreter in this window
Instead you are running the editor built into IDLE
You can use this editor to create Python scripts
Which are text files containing Python statements
When you type Python statements inside this window ...
the text will appear with the same highlighting colors ...
as in the interpreter window

But if you hit Enter or Return you just go down to the next line
The Python statement is not executed like it was in the interpreter
You can run the script you created
But only if you first save the file
To do this, go to the File menu and click and drag to down to Save
This will bring up a dialog box

But here you have to be careful
You have to save it in the right directory ...
or you will have a hard time finding it later ...
when you need to copy it to the Unix machine
I suggest you first create a python directory inside your Documents directory
Save all your scripts in this python directory
So you will know where to find them when you move them to pe15.cs.umb.edu
I have already created a python directory
So I will select that directory

Now I have to give the script file a name

And save it
When I do you can see in the title of the editor window
That the file has the name hello.py

All Python files have to have a .py extension
But I did not type it in when I named the file
The editor automatically supplied the .py extension

Running a Script in IDLE

Now that I have saved the file I can run it
This is done inside the interpreter window
Select "Run Module" from the Run menu
The Python interpreter window now moves in front ...
and the script is run inside the interpreter window

Changing a Python Script

What if you want to change a script?
The first thing you need to do is run IDLE
This will bring up the interpreter window

In the File menu click and drag down to Open

Select the python directory

Then select the file and double click

The file will appear inside an editor window

This windows allows you make any changes you need

Two Ways to Run Python

There are two ways to use Python
- Interactively
- Writing Python scripts
They are very different in the way they work
And they are used for different purposes
When you first open IDLE you see the interpreter window
In this window you can type a Python statement ...
and then hit Enter to run that statement
You can only run one statement at a time
This is called the interactive mode
It is mostly used for learning Python ...
and experimenting with features of the language
But when you want to use Python to do some real work ...
you will write a script
The scripts can have as many statements as you need
And when you run the script all statements are executed
Scripts can be run inside IDLE
But you can also run them at the command line
And that is how they are usually run by IT people

Python in Class Exercises

The first several Class Exercises have two parts
First, I ask you to type Python statements directly into the IDLE interpreter window
This will give you a chance to see how they work in Python ...
and give you immediate feedback when you make a mistake
In the beginning you will make a lot of mistakes
But you will get better as you go along
This is good practice for you
But I cannot see what you have done
So I can't assign you a score
That is why the second part asks you to create script ...
and copy it to pe15.cs.umb.edu
On pe15.cs.umb.edu I can see your script ...
and give it a score

Running Python in Interactive Mode

In interactive mode, you can use the Python interpreter as a calculator
```
>>> 5 + 6
11
>>> 6 - 5
1
>>> 3 * 5
15
>>> 4.1 / 2
2.05
```
When writing code we often need to store a value that will be needed later
To make this possible, all computer languages have variables
A variable is a place in memory with a name, that holds a single value
Giving a value to a variable is called assignment
In Python, the assignment operator is the equal sign, =
```
>>> a = 5
>>> b = 6
>>> a * b
30
>>> a - b
-1
```
If you type something that is not a legal Python statement you will get an error
```
>>> a $ b
  File "<stdin>", line 1
  a $ b
    ^
SyntaxError: invalid syntax
```
If you make a mistake, simply type the command again ...
and Hit Enter

Python on Unix

Everything you can do in IDLE ...
can be done on the Unix command line

To run Python in interactive mode type python3 and hit Enter

$ python3 
Python 3.8.10 (default, Nov 26 2021, 20:14:08) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 3
>>> b = 2
>>> a + b
5
>>>

You leave interactive mode by entering exit()
You can run a Python script using the following format
```
python3 FILENAME
```
So this is how to run hello.py
```
$ python3 hello.py 
Hello world!
```

Scripts versus Interactive Mode

In general, anything you can do in interactive mode you can also do in a script
And vice-versa
But there are two important differences between them
If you have defined a variable in an interactive session ...
it will disappear the moment you leave
The second difference involves printing values
In interactive mode, once you have assigned a value to a variable ...
you can print its value, just by typing the variable name
```
>>> a = 5
>>> a
5
```
This does not work with scripts

Using FileZilla

In order to move you Python scripts to pe15.cs.umb.edu you will need to use FileZilla
When you open FileZilla you will see a window like this

At the top of the window are four fields you must fill in
- Host
- Username
- Password
- Port
Host is the domain name of the machine to which you are connecting
We use pe15.cs.umb.edu
In the next box, enter your Unix username
The third box is for your password
Enter 22 in the last box
Then click the QuickConnect Button
The first time you do this, you will see this

Click Save Password and OK
When you do you will see the following

This is a security check
The alert box is saying that this is the first time you have connected here
Click Always Trust this Host to proceed
But if you see this in the future something is terribly wrong ...
and you had better contact the Class Assistant
Normally you just click OK
Then you should see something this

The top pane shows the connection steps
If there is a problem it will show up in red here
The area below shows 4 panes
Two on the left and two on the right
The leftmost two panes show your machine
The rightmost show the Unix machine
In each set the topmost pane allows you to select a directory
And the bottom-most shows you what is inside that directory
You will be using FileZilla to move files from your machine on the left ...
to the Unix machine on the right
I need to find my it116 directory on pe15.cs.umb.edu
First I click on my home directory ghoffman

The I scroll down until my it116 directory comes into view

When I double_click on the it116 directory ...
the two right hand panes change

The bottom right pane shows my empty it116 directory
If I right-click in this pane ...
I will get a menu that allows me to create a directory

I need to change "New directory" into the proper directory name

Then click OK
This will create the new directory

Double-click on the ex directory
To enter that directory
And repeat the above procedure to create an ex2 directory

Now we need to locate the file we want to copy
First I double-click on my home directory glenn

Then scroll down to my Documents directory

In the bottom pane I can double-click on the python directory

To see the ex2.py file
I want to move to Unix

Now I click and drag the ex2.py file
To the ex2 directory on Unix

Today's Class Exercise

The Class Exercises give you hands on experience with Python
The exercise asks you to run Python in interactive mode
And to create the ex2.py script
You can do both on your own machine
But the script must be copied to the correct directory the Unix machine pe15.cs.umb.edu
To do the Class Exercise for today you need to use your laptop
You will use it to connect to pe15
See the Class Exercise for details
If you have not registered for this class on the CS portal ...
First I click on my home directory ghoffman

The I scroll down until my it116 directory comes into view

When I double_click on the it116 directory ...
the two right hand panes change

The bottom right pane shows my empty it116 directory
If I right-click in this pane ...
I will get a menu that allows me to create a directory

I need to change "New directory" into the proper directory name

Then click OK
This will create the new directory

Double-click on the ex directory
To enter that directory
And repeat the above procedure to create an ex2 directory

Now we need to locate the file we want to copy
First I double-click on my home directory glenn

Then scroll down to my Documents directory

In the bottom pane I can double-click on the python directory

To see the ex2.py file
I want to move to Unix

Now I click and drag the ex2.py file
To the ex2 directory on Unix

Today's Class Exercise

The Class Exercises give you hands on experience with Python
The exercise asks you to run Python in interactive mode
And to create the ex2.py script
You can do both on your own machine
But the script must be copied to the correct directory the Unix machine pe15.cs.umb.edu
To do the Class Exercise for today you need to use your laptop
You will use it to connect to pe15
See the Class Exercise for details
If you have not registered for this class on the CS portal ...
First I click on my home directory ghoffman

The I scroll down until my it116 directory comes into view

When I double_click on the it116 directory ...
the two right hand panes change

The bottom right pane shows my empty it116 directory
If I right-click in this pane ...
I will get a menu that allows me to create a directory

I need to change "New directory" into the proper directory name

Then click OK
This will create the new directory

Double-click on the ex directory
To enter that directory
And repeat the above procedure to create an ex2 directory

Now we need to locate the file we want to copy
First I double-click on my home directory glenn

Then scroll down to my Documents directory

In the bottom pane I can double-click on the python directory

To see the ex2.py file
I want to move to Unix

Now I click and drag the ex2.py file
To the ex2 directory on Unix

Today's Class Exercise

The Class Exercises give you hands on experience with Python
The exercise asks you to run Python in interactive mode
And to create the ex2.py script
You can do both on your own machine
But the script must be copied to the correct directory the Unix machine pe15.cs.umb.edu
To do the Class Exercise for today you need to use your laptop
You will use it to connect to pe15
See the Class Exercise for details
If you have not registered for this class on the CS portal ...
you will not be able to log in

Course Work

New Material

Readings

Homework 1

Unix Account and Class Directory

Help with Creating a Unix Account

Questions

Course Work

Assignments

Submitting Assignments

Working on Assignments

Software for the Class

Class Assistant

New Material

Files

Directories (Folders)

Working With Files

Your Unix Course Directory

Types of Programming Languages

Python

Downloading Python

Running IDLE

Syntax Highlighting

Creating a Python Script

Running a Script in IDLE

Changing a Python Script

Two Ways to Run Python

Python in Class Exercises

Running Python in Interactive Mode

Python on Unix

Scripts versus Interactive Mode

Using FileZilla

Today's Class Exercise

Today's Class Exercise

Today's Class Exercise

Class Exercise

Attendance