IT 116: Introduction to Scripting

IT 116: Introduction to Scripting
Class 2

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.

Trouble?

Has anyone had any trouble registering for this class or anything else?

Today's Class

Today I will show you how to use the IDLE program and exlain it's two parts.

I will also show you how to use FileZilla to copy files from your machine to pe15.

Course Requirements

Unix Account

In this class you will be writing short programs in the Python computer language
You will create these programs on your computer
But I cannot see what's on your machine
To allow me to score your programs you must copy them to pe15 ...
which is a Linux computer on the CS department network
To work on pe15 you must have a Unix account
Each each of you must have your own Unix account ...
which is your identity when you are connected to pe15
Each account has a password that you must not share
To create an account go to http://www.cs.umb.edu/~ghoffman/linux/cs_portal.html#creating_unix_account.
and follow the instructions you will find there

Your Home Directory

Each account has a home directory that belongs to you and you alone
A directory is what you probably call a "folder"
A directory holds files and other directories
When you first connect to pe15 you will be inside your home directory
You are the only one who can make changes in this directory
Inside your home directory is the entry it116
This is a link to your class directory

Your Class Directory

If you have registered for this class ...
as I asked you to do in Class Exercise 1 ...
you will have a class directory for this course
The class directory is in a special place in the filesystem ...
that makes it easy for me to find your work
All work for this class must be copied to your it116 class directory
I will show you how to do this later in this class
If you have not registered for this class on the CS Portal ...
go to https://portal.cs.umb.edu, log in ...
click the check box for my section of this course, and click submit

Help with Unix Account or Class Directory

If you have difficulty creating an account or a class directory ...
you must get help immediately
You will not be able to do any work in this class ...
until you have both
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

Course Work

Assignments

There are two types of assignments for this course
- Class Exercises
- Homework assignments
In the Class Exercise you simply copy some Pyhton statements ...
into a file on your machine
This will give you some practice writing and fixing Python programs
For homework assignments you write your own Python files ...
following instructions in the assignment
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

The assignments ask you to write Python programs
You will create these files on your machine and test them to make sure they work
If they don't work, you must fix the code to correct the problem
If you need help with this you can
- See me after I finish talking in class
- Come to my Zoom Office hours
- Contact the Class Assistant
- Ask another student in this class
The program file must be copied to the correct directory inside your class directory
Today's Class Exercise will ask you to create two directories inside your class directory
- An hw directory for homework assignments
- An ex directory for Class Exercise files
For each homework file you must create an new directory for it under the hw directory
The name of this directory must be "hw" followed by the homework number
You must do the same for each Class Exercise file
So working on an assignment has two phases
First you create the file on your machine and get it to work
This you create a directory for it in either the hw or ex directories ....
and copy the file to the correct directory

Software for the Class

You need different software for each phase of your work
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 Python programs
For the second phase you need FileZilla
You will need FileZilla to create a directory for the assignment ...
and to copy your file to that directory
You will find instructions here
If you want to run your program on pe15.cs.umb.edu you need an SSH client
The SSH client allows you to log in to a Unix machine from your computer
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

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 drives and thumb drives (SSDs)
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 disk 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 diagram of all the directories on a machine ...
it would look like a pyramid

The top directories of a Linux machine might look like this

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 it 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 my collection scripst will not be able to find them

Types of Programming Languages

Programming langages allow you to write programs ...
that will do what yout want them to do
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
Source code file is text file 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
The executable 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 creates the executable file hello ...
which I can run on the Unix machine
```
$ ./hello 
Hello, world!
```
Compiled languages are designed for big programming projects
But 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
They are not a fussy as compiled languages ...
which makes them easier to use for people who are not programmers
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
This will create a Python directory on your machine
Inside this directory you will find an application named IDLE

The IDLE Program

We will be using IDLE extensively in this class
But IDLE has two different parts
- The interpreter
- The editor
Each part has its own window ....
and does different things
When you first run IDLE you are in the interpreter window
This window is used for learning and experimentation
You type a Python statement inside the window ...
hit Return or Enter ...
and the interpreter tries to run the line
The interpreter window does not create files
For that you need the editor window
Each window has its own set of menus ...
which are similary ...
but different

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

The statement has printed the text inside the parentheses ...
and issued a new prompt ...
to say it is ready for your next statement
When you work in this window ...
you are talking directly to the Python interpreter
This is called running Python in interactive mode
You type a Python statement ...
and the python interpreter in IDLE executes it

Syntax Highlighting

Notice that different parts of the 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" in the File menu ...
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 Python editor
This is the part of IDLE you use to create Python files ...
that you will uplaod to pe15
These Python files are sometimg called scripts ...
which means text files containing statements in the Python lanuage
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 window
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 the filename ...
at the top of the editor window
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

Fixing Errors in a Script

Sometimes when you run a Python script you get an error
When this happens you will see a big red error message ...
in the interpreter window

The last line of the error message is the most useful
It says that the script has a typo
The word "print" is misspelled
All you have to do is go back to the editor window ...
and fix the spelling
Then run the script again ...
to make sure it works
When learning a computer language your code will often produce errors
But you will make fewer mistakes as you go through this course

Changing a Python Script

What if you want to change a script you have already written?
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

IDLE Has Two Different Parts

IDLE is a single program ...
that has two different components
The first part allows you to write a single Python statement ...
hit Enter or Return ...
and have the Python interpreter run that statement
This happens in the first window you see when you open IDLE
In this window you are talking directly to the Python interpreter
The second part is the editor
In this window you write your Python programs ...
and save them to a directory on your computer
After you have saved them ...
you run them in the interpreter window ...
to see if they work properly

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 ...
in the IDLE editor window ...
run it to make sure it works ...
and copy it to pe15.cs.umb.edu
On pe15.cs.umb.edu I can run your script ...
and give it a score

Using FileZilla

In order to move your 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 input boxes you must fill in
- Host
- Username
- Password
- Port
Host is the network name of the machine you are connecting to
Here you should enter 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 message in the future something is terribly wrong ...
and you had better contact the operator at operator@cs.umb.edu
Normally you just click OK
Then you should see something this

The top pane shows the connection steps ...
with several Status lines
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
Above each set of panes are lines that shows was directory you are in
The leftmost line has the label "Local site:"
The righmost is labeled "Remote site:"
Local site is your machine
Remote site is pe15
You will normally be using FileZilla to move files from your machine on the left ...
to the Unix machine on the right
Now you need to find your it116 directory on pe15.cs.umb.edu
First click on your home directory

Then scroll down until the it116 directory comes into view

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

The bottom right pane shows what is in the it116 directory
If you right-click in the white space in this pane ...
You will get a menu that allows you to create a directory

Click on "New Directory" and a dialog box appears

You need to change "New directory" to "ex
Then click OK
This will create the ex directory

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

Enter the ex2 directory by double-clicking on it

Now you need to locate the file you want to copy
If you followed my sugggestion ...
its should be in a python directory ...
inside your Documents directory
Click and drag the ex2.py file ...
from the bottom left pane ...
to the bottom right pane
This is what you should see

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 do this on your own machine
But the script must be copied to the correct directory on the Unix machine pe15.cs.umb.edu
Follow the procedure I showed you above to do this

Course Requirements

Course Work

New Material

Readings

Homework 1

Trouble?

Today's Class

Course Requirements

Unix Account

Your Home Directory

Your Class Directory

Help with Unix Account or Class Directory

Course Work

Assignments

Submitting Assignments

Software for the Class

New Material

Files

Directories (Folders)

Working With Files

Types of Programming Languages

Python

Downloading Python

The IDLE Program

Running IDLE

Syntax Highlighting

Creating a Python Script

Fixing Errors in a Script

Changing a Python Script

IDLE Has Two Different Parts

Python in Class Exercises

Using FileZilla

Today's Class Exercise

Class Exercise

Attendance