GUIDE TO PROGRAMMING WITH PYTHON

Guide to Programming with
Python
Chapter One
Getting Started: The Game Over Program

What is programming
• Computer Science- The study of theoretical foundations of
information and computation and their implementation and
application in computer systems. It is mainly about
computational problem solving.
• The process of learning to program is an excellent
opportunity to practice problem-solving skills.
• Program: A computation expressed in a programming
language as a set of instructions to be carried out by a
computer.
• The computation might be something mathematical, such
as solving a system of equations or ﬁnding the roots of a
polynomial, but it can also be a symbolic computation, such
as searching and replacing text in a document or (strangely
enough) compiling a program!

• A program basically contains following instructions
• The details look different in different languages, but these
few basic instructions appear in just about every language
-input: Get data from the keyboard, a ﬁle, or some other
device.
-output: Display data on the screen or send data to a ﬁle or
other device.
-Calculations: Perform basic mathematical operations like
addition and multiplication.
-Conditional execution: (Boolean tests), Check for certain
conditions and execute the appropriate code.
Repetition: Perform some action repeatedly, usually with
some variation.

• Program execution: The act of carrying out the
instructions contained in a program.
• Programming language: Is an artificial language, a
systematic set of rules used to describe computations in a
format that is editable by humans.
– This textbook teaches programming in a language Python

Objectives
•
•
•
•
•

Introduce Python
Demonstrate how to install Python
Explain how to print text to the screen
Describe comments and how to use them
Demonstrate Python’s development environment,
IDLE, using it to write, edit, run, and save programs

Guide to Programming with Python

5

Examining the Game Over Program

Figure 1.1: Game Over Program Output
The all-too familiar words from a computer game

6

Examining the Game Over Program
(continued)
• “Hello World” program: By tradition, prints "Hello,
world!”
– Often used as first program

• Console window: Provides a text-based interface
to operating system


7

Introducing Python
•
•
•
•
•

Powerful yet easy to use programming language
Developed by Guido van Rossum
First released in 1991
Named after comedy troupe Monty Python
An alarming number of references to spam, eggs,
and the number 42 in documentation


8

Python Is Easy to Use
• High-level language: Separate from the low-level
processor operations; closer to human language
than machine language
• "Programming at the speed of thought"
• Increases productivity
– Python programs three to five times shorter than
Java
– Python programs five to ten times shorter than C++


9

Python Is Easy to Use (continued)
• Python Program
print "Game Over!"

• C++ Program
#include <iostream>
int main()
{
std::cout << "Game Over!" << std::endl;
return 0;
}


10

Python Is Powerful
• Used by large organizations
– NASA
– Google
– Microsoft

• Used in published games
– Battlefield 2
– Civilization IV
– Disney’s Toontown Online


11

Python Is Object-Oriented
• Object-oriented programming (OOP):
Methodology that defines problems in terms of
objects that send messages to each other
– In a game, a Missile object could send a Ship
object a message to Explode

• OOP not required, unlike Java and C#


12

Python Is a “Glue” Language
• Can be integrated with other languages
– C/C++
– Java

• Use existing code
• Leverage strengths of other languages
– Extra speed that C or C++ might offer


13

Python Runs Everywhere
• Platform independent: Independent of the
specific computer operating system
• Python runs on
–
–
–
–
–

Windows
DOS
Mac OS
Linux
Many more


14

Python Has a Strong Community
• As an approachable language, has approachable
community
• Python Tutor mailing list
– http://mail.python.org/mailman/listinfo/tutor
– Perfect for beginners
– No actual "tutors" or "students"


15

Python Is Free and Open Source
• Open source: Publicly available; open source
software typically programmed by volunteers;
anyone can use source code without fee
• Can modify or even resell Python
• Embracing open-source ideals is part of what
makes Python successful


16

Setting up Python on Windows
•

Using the CD-ROM that came with the book
1. Find the Python Windows Installer, Python2.3.5.exe, under the Software section
2. Click on the Install Python 2.3.5 from this CDROM link and run the installer
3. Accept the default configuration
4. Version 2.3.5 installed in the C:Python23 folder


17

Setting up Python on Windows
(continued)

Figure 1.2: Python Installation Dialogue under Windows
Your computer is soon to be home to Python.

18

Setting up Python on Other Operating
Systems
• Download appropriate version from Python home
page at www.python.org
• Linux
– Python may already be installed
– Test: try running python at command prompt
– If not installed, go to Python home page to download

• Mac OS
– After Python page, visit MacPython page at
http://homepages.cwi.nl/~jack/macpython/index.html


19

Introducing IDLE
• Integrated Development Environment (IDE):
Application that helps software developers write
programs
– Like a word processor for your code

• IDE that ships with Python
• Has two “modes”: Interactive and Script


20

Programming in Interactive Mode

Figure 1.4: Python in interactive mode
Python awaits your command.

21

(continued)
• Great for immediate feedback
– Test a simple idea
– Remember how something works

• Open Python in interactive mode
– In Windows, from the Start menu, choose Programs,
Python 2.3, IDLE (Python GUI)


22

(continued)
• At command prompt (>>>), type: print
• Python responds with: Game Over


"Game Over"

23

(continued)
Statement can display a string
• String: Sequence of characters
• Statement: Single unit in programming language
that performs some action
• print

– print "Game Over"

• Expression: Something which has a value or that
can be evaluated to a single value
– "Game Over"
– 7 + 2

• Code: Sequence of programming statements

24

(continued)
• Syntax highlighting: Displaying programming
code in different colors or fonts, according to the
category of each item
• Errors
– Computers take everything literally
– primt "Game Over" produces an Error Message:
SyntaxError: invalid syntax

– Syntax error: Error in the rules of usage; often a
typo
– Bug: Error in programming code

25

Programming in Script Mode

Figure 1.5: Python in script mode
Your blank canvas awaits.

26

(continued)
• Great for programs you want to run later
– Write, edit, save, and load programs
– Like word processor for your programs
• Find and replace
• Cut and paste

• Open a script window
– In interactive window, select File menu, New
Window


27

(Continued)
• Write program
– In script window, type print "Game Over"

• Save program
– Select File, Save As, name game_over.py
– Always save before running

• Run Program
– Select Run, Run Module
– Results displayed in interactive window


28

(continued)

Figure 1.6: Python after a script has been run
The results of running the Game Over program

29

The Game Over Program
# Game Over
# Demonstrates the print command
print "Game Over"
raw_input("nnPress the enter key to exit.")


30

The Game Over Program (continued)
• Comment: Note in source code meant only for
programmers; ignored by computer
– Start comment with #
– Use opening block of comments

• Blank Lines
– Also (generally) ignored by computer
– Use for readability; keep related code together

• Console Window
– Final line keeps console window open

31

Summary
• Python is a high-level, object-oriented
programming language that’s powerful yet easy to
use
• Python can interface with other programming
languages
• IDLE is Python’s standard IDE
• IDLE has an interactive mode that offers immediate
response to Python code
• IDLE has a script mode that allows programmers to
write, edit, load, save, and run their programs

32

Summary (continued)
• A string is a sequence of characters
• A statement is a single unit of programming that
performs some action
• The print statement displays strings on the screen
• An expression is something which has a value or
that can be evaluated to a single value
• Syntax highlighting is displaying programming code
in different colors or fonts, according to the
category of each item

33

Summary (continued)
• A syntax error is a violation of the grammar of a
programming language; often caused by a typo
• A bug is an error in programming code
• A comment is a note in source code meant only for
programmers; ignored by computer
• Comments start with #
• You should use an opening block of comments in
your programs to identify the programmer, the
creation date, and the program’s purpose

34

GUIDE TO PROGRAMMING WITH PYTHON

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