introduction to python programming course

Introduction to Python
● Using the textbook.
● Python environment.
● Interactive Python interpreter.
● Script Python files.
● Simple Python programs.
● Variable names.
● Python is case-sensitive.
● Input from keyboard and Output to the screen.
● Errors handling.
Slides are adapted from prof Radu I Campeanu

How to access the textbook/Demo
1. Sign in or create an account at learn.zybooks.com
2. Enter zyBook code: ITEC1610SaedniaWinter2025
3. Subscribe
● This is a short textbook usage session
○ https://vimeo.com/285133146/48bc90afb5
● It will illustrate how to read the textbook, how to practice with the existing question and answer
examples and how to work with the labs.
● Only the first chapter of the textbook will be utilized in this lecture.
● The work in this first chapter will not be included in your assessment.

What is a computer?
A computer is “an electronic machine” that is designed to deal with information/data
(store data, execute instructions to retrieve the data, and process it to run a certain
application).
It has 2 main components
● Hardware: CPU, memory, keyboard, mouse, hard drive….
● Software: a set of instructions that tells the hardware what to do and how to do it (i.e.,
web browser, Microsoft Word, a game..).

Recap on binary system
● All information in a computer is stored and managed as binary values.
● Unlike the decimal system, which has 10 digits (0 through 9), the binary
number system has only two digits (0 and 1).
● A single binary digit is called a bit .
● On many computers, each memory location consists of eight bits, or one byte, of
information. If we need to store a value that cannot be represented in a single byte,
such as a large number, then multiple, consecutive bytes are used to store the data.

Downloading Python
●Python was invented by Guido van Rossum in 1991.
●For this course you need install Python as an application on your local computer. Mac and Linux operating
systems usually include Python, while Windows does not.
●You can download the latest version of Python for free from https://www.python.org on your home PC.
●Python is already installed in the DB labs.
●If you want to work with an Integrated Development Environment (IDE), I recommend to download
VSCode from https://code.visualstudio.com/download

Big Concept
● Programming is a recipe: understand the problem, design it, then code it!
Computers are not different to any invented appliance. They depend on these 3 steps:
● Receive an input
● Run some logical processing
● Generate some output
Inputs Outputs
Process
{…..
……
……}
Can you think of apps that do no follow that rule?

Computer Program Basics
A computer program consists of instructions executing one at a time. Basic instruction types are:
● Input: A program gets data, perhaps from a file, keyboard, touchscreen, network, etc.
● Process: A program performs computations on that data, such as adding two values.
● Output: A program puts that data somewhere, such as to a file, screen, or network.
Programs use variables to refer to data, like a, b, and c below. The name is due to a variable's value "varying" as a
program assigns a variable like c with new values.
a=2 ( = is the assignment operator)
b=5
c=a+b
c=2*c
print(c)

Python interpreter
●An interactive interpreter is a program that allows the user to execute one line of code at a time.
●In this course we shall use the black screen window created on your home PC by entering the ‘cmd’
command in the Start button window. In the DB labs the black screen window appears automatically.
●In the black screen window enter the command ‘python’. The interactive Python interpreter displays a
prompt (‘>>>’) that indicates the interpreter is ready to accept code.
●We shall not use this interactive interpreter in this course because we want to learn to write multi-line
programs, saving these programs in script files.

An Example with the Python interpreter
●The example shown below calculates your final mark in this course based on labs, two assignments, midterm test and final exam.
>>> labs = 80
>>> a1 = 100
>>> a2 = 90
>>> midterm = 70
>>> finalExam = 80
>>> finalMark = labs*0.2 + a1*0.1 + a2*0.1 + midterm*0.4 + finalExam*0.2
>>> print(finalMark)
79.0
Note 1: The same result can be obtained with
>>> print(80+.2+100*.1+90*.1+79*.4+80*.2)
Note 2: The operator = is not the “mathematical equal sign”. It is an
assignment operator. In the first line 80 is assigned to the variable labs.

Another Example
●The example program below calculates a salary based on a given hourly wage, number of hours worked
per week, and the number of weeks per year.
>>> wage = 20
>>> hours = 40
>>> weeks = 50
>>> salary = wage * hours * weeks
>>> print(salary)
40000
>>> hours = 35
>>> salary = wage * hours * weeks
>>> print(salary)
35000

Python interpreter inside the textbook
●The textbook for this course has its own Python interpreter.
●This interpreter will be used to build your solutions for the labs.
●When your lab solution is correct you will receive a message.
●Only correct labs should be submitted.
●If you have hard time getting a correct solution move to another lab.

Creating a Python script file
●You can use a text editor, such as Notepad. Write the code:
●Save the newly created file as salary.py
Interpret and run the file with the command python salary.py
The output will be:
Salary is: 40000
New salary is: 35000
wage = 20
hours = 40
weeks = 50
salary = wage * hours * weeks
print('Salary is:', salary) # this creates an output line
hours = 35
salary = wage * hours * weeks
print('New salary is:', salary)

Create the script file with VSCode
●Click on the VSCode icon and then click on File and click on New
●Enter the same code as in the previous slide in the right window
●Click on File and then click on Save As to baptize the file as salary.py
●Click on click on Run
●You will see the output in the small window below the code

General rules re Python script files
●The name of the file usually shows the purpose of the program, but there are no strict rules related to naming
the files. A good idea is to keep the names short.
●Inside the Python script files each statement must occupy a separate line.
●Almost all words in Python should be written in the lower case. The only exception is in the lecture about
classes, where the class names have to start with a capital letter.
●Empty lines are allowed.
●Comments (starting with #) are ignored by the Python interpreter.
●In lecture 4 we shall introduce code indentation, which is a very important feature of Python. Until that lecture
all lines must start in the 1st column.

Variable names
● In the example already discussed hours, wage, weeks are variables. They correspond to
locations of memory where the user can enter data multiple times.
● Programmers generally choose names for their variables that are meaningful. Variable
names can be as long as you like. They can contain both letters and numbers, but they
can’t begin with a number.
● It is legal to use uppercase letters, but it is conventional to use only lower case for
variables names.
● The underscore character, _, can appear in a name. It is often used in names with multiple
words, such as your_name; the alternative is to write yourName.
● If you give a variable an illegal name, you get a syntax error:
>>> 76trombones = 'big parade’
SyntaxError: invalid syntax (because of ‘76’ )
>>> more@ = 1000000
SyntaxError: invalid syntax (‘@’ is illegal)
>>> class = 'Advanced’
SyntaxError: invalid syntax (‘class’ is a reserved word)

Python’s “variables” are really variables
In Python you do not have to announce what kind of data you want to enter in a variable. The variable is
adjusted to the data on the right side of the assignment operator =
The following program illustrates these ideas.
a=20
a=a+50
print(a)
a="hello"
a=a+" Tom"
print(a)
Output:
70
hello Tom
The variable a starts as a location to store integers and in the second part of the program it stores text/strings.
This feature of Python will not exist in Java.

Python is case-sensitive
●Variables names or reserved words are case sensitive. For example the interpretation of the code:
a=2
b=5
c=A+b
prinT(c)
will signal as errors the ‘A’ in the 3rd line and ‘print’ in the 4th line

Text Output
●Multiple lines output:
print(‘Hello everybody’)
print(‘My name is John’)
Important note: the quote character ‘ in PowerPoint or Word is different from the Notepad character,
which Python understands. Therefore when you get Python code from this Powerpoint file you must
copy/past it into Notepad before compiling it in Python. This is the reason why in each week of the
course you will find most examples in Notepad-created text files available under the “Python code” links.
●One line output:
print(‘Hello everybody’, end=' ')
print(‘My name is John’)

Text and Variable Output
●One line output:
salary=1000
print(‘My salary is’, end=‘ ‘)
print(salary) # print variable value
●Or:
print(‘My salary is:’, salary)
●Multiple output lines:
print(‘1n2n3’) # n is a special character which moves the cursor to the next line
print() # this creates an empty line of output

Input from the keyboard
● Enter text:
print('The name of my dog is:')
dog=input()
print(dog)
Method input() always provides a text coming from the keyboard
● Enter an integer:
print('My age is:')
age = int(input()) # convert the text to integer
print(age)
● A shorter but equally correct input line is:
age = int(input('My age is:'))
print(age)

Errors
●Syntax errors reported by the interpreter with the line number, but the message is not always clear; often the
error can be in the previous line of code. A good idea is to check your program after a small number of lines,
in small steps.
●Runtime errors are reported when the program attempt an impossible operation. For instance in the
execution of the line of code a = int(input()) the user enters from the keyboard the word ‘Bob’.

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