Essential Python 3

By Kevin Vans-Colina

This book is written to provide all the essential information to get you programming in Python 3. The book starts by running through the basics of the language before showing you how to use some of the powerful libraries included in Python 3.

• Language: English
• Publisher: Kevin Vans-Colina
• Release date: Jul 3, 2021
• ISBN: 9780463901809

Book preview

Essential Python 3

Copyright 2021 Kevin Vans-Colina

Thank you for downloading this ebook. This book remains the copyrighted property of the author, and may not be redistributed to others for commercial or non-commercial purposes. If you enjoyed this book, please encourage your friends to download their own copy from their favorite authorized retailer. Thank you for your support.

The author assumes no responsibility for errors, emissions or damages that result from using the information and programs in this book.

Published by Sorefoot Software 29/11/21

Distributed by Smashwords.

Contact: [e-mail]

Table of Contents

1. Introduction

2. What is Python

3. Getting Python

Install Python

Setting Up the Path

Running Python

4. Python 2

5. Python Basics

Using the Interpreter Interactively

Using the Interpreter with a Script

6. Python Help

7. Python Syntax

Identifiers in Python

Program Layout

Comments

8. Variables

Immutability

Numeric Variables

int (signed integers)

float (floating point real values)

Complex (complex numbers)

Strings

String Methods

String Formatting

Variable Scope and Namespaces

9. Data Types

Lists

Tuple

Dictionaries

10. Data Type Conversion

11. Operators

Arithmetic Operators

Comparison Operators

Assignment Operators

Bitwise Operators

Logical Operators

Membership Operators

Identity Operators

Operator Precedence

12. Program Flow Control

While Loop

For Loop

Offsets and Items

Continue Statement

Break Statement

Loop Statements and Else

If Statement

if / else Ternary Expression

13. Functions

Function Definition

Default Function Arguments

Variable Length Arguments

Anonymous Functions

Map Function

Filter Function

Reduce Function

14. Modules

Module Reloads

Locating Module Files

Module Data Hiding

__name__ and __main__

15. Classes and Objects

Class Definition

Static methods

Inheritance

Function Overloading

Overloading Operators

Class attributes

Garbage Collection

16. Input and Output

Screen Output

Keyboard Input

Opening Files for Reading and Writing

Writing to Files

Reading from Files

Closing Files

Binary Files

Moving around Files

File Attributes

Managing Files and Directories

17. Exceptions

try - except

try – finally

Exception Arguments

Raising Exceptions

18. Date and Time

Time Module

Formatted Time

DateTime Module

Calendar Module

19. Example Project – Software Bug Tracker

Issue Class

Project Class

20. Command Line Arguments

21. Configuration Files

22. Databases

SQL

23. XML

Simple API for XML (SAX)

Document Object Module for XML (DOM)

24. HTML Parsing

25. Tkinter- GUI

Overview

Widget Layout

Pack Manager

Place Manager

Grid Manager

Simple Form

Practical Form

Message Boxes

Dialogs

File Dialog

Menus

Resizing the form

Scroll Bars

26. Where Next?

27. Appendix 1-Interpreter Command Line Options

28. Appendix 2 – Reserved Words

29. Appendix 3– Bug Tracker Code

Issue.py

project.py

bugTracker.py

30. Appendix 4 – Simple Notepad 1

31. Appendix 5 – Simple Notepad 2

1. Introduction

This book is designed to give all the essential information to get you programming in Python. The book starts by running through the basics of the language before showing you how to use some of the powerful libraries included in Python, finally it will show you how to produce full applications with form based user interfaces.

2. What is Python

Python is an easy to learn programming language which particularly popular with the hobbyist it is also used by professional programs to write utilities. Python is an interpreted language which makes it a good choice for rapid application development.

Python has a clear defined syntax, a small set of keywords and a simple program structure, this allows the programmer to quickly learn how to program in Python. The simple syntax means that it is also easy to read which has the advantage that source code is easy to maintain.

Python has a large standard library this means that scripts can be used across multiple platforms without having compatibility issues. There are also a vast number of freely available libraries which allow you to use Python for virtually anything. Low level modules can easily be added to the Python interpreter by writing these modules in an compiled language such as C these modules run much faster. Finally GUIs can be generated in Python which can then be ported to many other operating systems.

Python also has support for objected orientated, structured and functional programming. It can be complied as byte code for larger programs or run as an interpreted language. It has high level dynamic data types and supports dynamic type checking. Memory management is taken care of automatically by Python.

Python is available on a wide variety of platforms including

Unix (Solaris, Linux, FreeBSD, AIX, HP/UX, SunOS, IRIX)

Win 9x/ NT /2000 / XP / Vista /Windows 7

Macintosh

OS/2

DOS

PalmOS

Windows CE

Acorn/RISB OS

BeOS

Amiga

Java virtual machine

.NET virtual machine

3. Getting Python

The best place to download a copy of Python is from the official web site which is http://www.Python.org. This is also a good source of documentation, news, current source code etc. This is probably the best place to get further information on keywords and libraries.

Install Python

If the binary for your platform is available then you can download it, if there is not a version for your platform then you can download the source code and compile it manually.

If you have downloaded the binary then it can simply be installed using the installer.

Setting Up the Path

To make life easier when working with Python it is worth setting up the path variable for your platform, the path variables tells the computer where to look for executable files in this case the Python interpreter.

Note the path in the following examples may vary so you might have to check where your copy of Python was installed.

Unix / Linux Path

Csh shell

setenv PATH $PATH:/usr/local/bin/Python

Bash shell (Linux)

Export PATH= $PATH:/usr/local/bin/Python

sh or ksh shell

PATH=$PATH:/usr/local/bin/Python

Windows Path

In the command prompt type

path %path%;C:\Python

Running Python

Python can be run interactively from the interpreter, from the command line using a script or from an IDE.

To run the interpreter from the start menu open a command window then type

python

The Python interpreter should run and something similar to the following should be displayed on the screen, if it doesn't then check your path variable is correctly pointing to where Python was installed.

Python 3.2.3 (default, Apr 11 2012, 07:15:24) [MSC v.1500 32 bit (Intel)] on win32

Typehelp, copyright, credits or licence for more information

To run a Python script directly type python followed by the program name

python helloworld.py

The command input above will cause a Python script called helloworld.py to be run.

There are numerous Integrated Development Environments available for Python (IDLE, PythonWin, PyCharm) these allow program creation and allow you to run the Python programs directly as you develop them, although any text editor can also be used to create programs using an IDE will speed up developing scripts.

4. Python 2

This book is written for Python 3 which is the latest version of Python. Python 3.x is not fully compatible with the previous versions of Python. Python 3.x breaks some of the features of Python 2.x to clean up and improve the constancy of the language. The major changes are described below but the Python website will give you full details if you want to make your code backward compatible.

The print statement has been changed into a function print() and now uses keyword arguments to replace the syntax used by the old print statement.

The input function raw_input() has been changed to input().

Integers now only have a single type.

Divisions now by default return floating point values, the whole number can be returned by using a double backslash ( x = y // z).

Strings are all Unicode rather than 8 bit character based.

Some of the APIs return views rather than lists for example the dictionary dict.keys().

Not equal can only be expressed by != , <> has been removed.

String formatting no longer uses the % operator.

To future proof modules it is better to update libraries to Python 3.x rather than write your code in Python 2.x.

5. Python Basics

Using the Interpreter Interactively

Start up the interpreter and type

print ('Hello World')

followed by 'enter', the interpreter should display a new line

Hello World

The interpretor has interpreted the print command and has printed 'Hello World' to the screen.

To exit the interpretor use type exit() or quit();

Using the Interpreter with a Script

While the interpreter can be used interactively this is not very useful if every time you want to run a program you need to type all the commands in one line at a time. For this reason writing Python code in script files makes a lot more sense.

To write a simple script use