1. introduction to python

1.1 Introduction to Python
1ARULKUMAR V AP/CSE SECE

Objectives
2
 To write and run a simple Python program.
 To explain the basic syntax of a Python program (§1.5).
 To describe the history of Python (§1.6).
 To explain the importance of, and provide examples of,
proper programming style and documentation (§1.7).
 To explain the differences between syntax errors,
runtime errors, and logic errors (§1.8).
 To create a basic graphics program using Turtle (§1.9).
ARULKUMAR V AP/CSE SECE

What is Python?
General Purpose Interpreted Object-Oriented
3
Python is a general purpose programming language.
That means you can use Python to write code for
any programming tasks. Python are now used in
Google search engine, in mission critical projects in
NASA, in processing financial transactions at New
York Stock Exchange.

What is Python?
4
Python is interpreted, which means that python
code is translated and executed by an interpreter
one statement at a time. In a compiled language, the
entire source code is compiled and then executed
altogether.

What is Python?
5
Python is an object-oriented programming
language. Data in Python are objects created from
classes. A class is essentially a type that defines the
objects of the same kind with properties and
methods for manipulating objects. Object-oriented
programming is a powerful tool for developing
reusable software.

Python’s History
• created by Guido van Rossum in Netherlands in
1990
• Open source

Python 2 vs. Python 3
Python 3 is a newer version, but it is not
backward compatible with Python 2. That
means if you write a program using Python
2, it may not work on Python 3.

Launch Python

Launch Python IDLE

Run Python Script

A Simple Python Program
# Display two messages
print("Welcome to Python")
print("Python is fun")
11
Run
Welcome
Listing 1.1
IMPORTANT NOTE:
(1) To enable the buttons, you must download the entire slide
file slide.zip and unzip the files into a directory (e.g.,
c:slide). (2) You must have installed Python and set python
bin directory in the environment path. (3) If you are using
Office 2010, check PowerPoint2010.doc located in the
same folder with this ppt file.

Creating and Editing Using Notepad
To use Notepad, type
notepad Welcome.py
from the DOS prompt.

Trace a Program Execution
13
Execute a statement
animation

Trace a Program Execution
14
Execute a statement
animation

Two More Simple Examples
15
RunWelcomeWithThreeMessages
RunComputeExpression

Supplements on the
Companion Website
• See Supplement I.B for installing and
configuring Python
• See Supplement I.C for developing Python
programs from Eclipse
www.cs.armstrong.edu/liang/py
16
Companion
Website

Anatomy of a Python Program
• Statements
• Comments
• Indentation

Statement
A statement represents an action or a sequence of
actions. The statement print("Welcome to Python") in
the program in Listing 1.1 is a statement to display the
greeting "Welcome to Python“.
18

Indentation
The indentation matters in Python. Note that the
statements are entered from the first column in
the new line. It would cause an error if the
program is typed as follows:
19

Special Symbols
20
Character Name Description
()
#
" "
''' '''
Opening and closing
parentheses
Pound sign
Opening and closing
quotation marks
Opening and closing
quotation marks
Used with functions.
Precedes a comment line.
Enclosing a string (i.e., sequence of characters).
Enclosing a paragraph comment.

Programming Style and
Documentation
• Appropriate Comments
• Proper Indentation and Spacing
Lines

Appropriate Comments
Include a summary at the beginning of the
program to explain what the program does, its key
features, its supporting data structures, and any
unique techniques it uses.
Include your name, class section, instructor, date,
and a brief description at the beginning of the
program.

Proper Indentation and Spacing
• Indentation
– Indent four spaces.
– A consistent spacing style makes programs clear
and easy to read, debug, and maintain.
• Spacing
– Use blank line to separate segments of the
code.

Programming Errors
• Syntax Errors
– Error in code construction
• Runtime Errors
– Causes the program to abort
• Logic Errors
– Produces incorrect result

Getting Started with GUI Programming
Why GUI? Turtle Tkniter
25
GUI is a great pedagogical tool to motivate studetns
and stimulate student interests in programming.

26
A simple way to start graphics programming is to
use Python built-in Turtle package.
Run
A Turtule Example

27
Later in the book, we will also introduce Tkinter for
developing comprehensive GUI applications.
Run
A Tkinter Example

1. introduction to python

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