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Learning Python Application Development

Chapter 1. Developing Simple Applications

Python is one of the most widely used dynamic programming languages. It supports a rich set of packages, GUI libraries, and web frameworks that enable you to build efficient cross-platform applications. It is an ideal language for rapid application development. Such fast-paced development often comes with its own baggage that could bring down the overall quality, performance, and extensibility of the code. This book will show you ways to handle such situations and help you develop better Python applications. The key concepts will be explained with the help of command-line applications, which will be progressively improved in subsequent chapters.

This chapter will be an introductory one. It will serve as a refresher to Python programming. That being said, it is expected you have some knowledge of Python language, as well as object-oriented programming (OOP) concepts.

Here is how this chapter is organized:

We will start with installation prerequisites and set up a proper environment for Python development.
To set the tone right for the rest of the book, the next section will be a brief introduction to the high fantasy theme of the book.
What follows next is our first program. It is a simple text-based fantasy game, presented as a Python script.
We will add some complexity to this game and develop an incremental version of the game using simple functions.
Moving ahead, we will add more features to the game and redesign the code by applying OOP concepts.
The last topic will briefly cover Abstract Base Classes (ABCs) in Python.

The code explanation will be a bit verbose. More experienced readers can breeze past the examples and go to the next chapter, but be sure to understand the theme of the book and review the code in the ch01_ex03.py file. In the next few chapters, you will learn techniques to progressively improve this code.

Installation prerequisites

Let's make sure that we have installed the prerequisites. Here is a table that summarizes the basic tools we need for this chapter and beyond; more verbose installation instructions follow in the next section:

Tool	Notes
Python 3.5	The code illustrated in this book is compatible with version 3.5. See the next table for available Python distributions. Supporting code bundles also provide 2.7.9 compatible files.
pip (package manager for Python)	The pip is already available in the official distribution for versions 3.5 and 2.7.9.
IPython	Optional installation. IPython is an enhanced Python interpreter.
Integrated development environment (IDE)	Use the Python editor or any IDE of your choice. Some good IDEs are listed in a table later in this chapter.

In subsequent chapters, we will need to install some additional dependencies. The Python package manager (pip) will makes this a trivial task.

Tip

Have you already set up the required Python environment or know how to do it? Just skip the setup instructions that follow and move on to the The theme of the book section, where the real action begins!

Installing Python

There are two options to install Python. You can either use the official Python version or one of the freely available bundled distributions.

Option 1 – official distribution

For Linux or Mac users, Python is probably already installed on your system. If not, you can install it using the package manager of your operating system. Windows OS users can install Python 3.5 by downloading the Python installer from the official Python website:

During the installation process, just make sure to select the option that adds Python 3.5 to the system environment variable, PATH, as shown in the preceding screenshot. You can also visit the official Python website, https://www.python.org/downloads, to get the platform-specific distribution.

Option 2 – bundled distribution

Alternatively, there are several freely available Python distributions that bundle together useful Python packages, including pip and IPython. The following table summarizes some of the most popular Python distributions, including the official one:

Distribution	Supported platforms	Notes
Official Python distribution https://www.python.org	Windows, Linux, Mac	Freely available Versions 2.7.9 and 3.5 include pip by default
Anaconda http://continuum.io	Windows, Linux, Mac	Freely available Includes pip, IPython and Spyder IDE Bundles packages primarily for science, math, engineering, and data analysis
Enthought Canopy Express https://www.enthought.com/canopy-express/	Windows, Linux, Mac	Freely available Includes pip and IPython Integrates a Python code editor and application development platform
Python(x, y) https://python-xy.github.io/	Windows	Freely available Includes pip, IPython, and Spyder IDE

Python install location

Let's briefly talk about the path where Python is installed, and how to make sure python is available as a command in your terminal window. Of course, things will widely vary, depending on where you install it and which Python distribution you choose.

Tip

The official Python documentation page has comprehensive information on setting up the Python environment on different platforms. Here is a link, in case you need further help beyond what we have covered: https://docs.python.org/3/using/index.html.

Unix-like operating systems

On a Unix-like operating system such as Linux, the default location is typically /usr/bin/python or /usr/local/bin/python.

If you used your operating system's package manager to install Python, the command python or python3 should be available in the terminal window. If it isn't, you need to update the PATH system environment variable to include the directory path to the Python executable. For example, if you have a Bash shell, add the following to the .bashrc file in your user home directory:

export PATH=$PATH:/usr/bin/

Specify the actual path to your Python installation in place of /usr/bin.

Windows OS

On Windows OS, the default Python installation path is typically the following directory: C:\Users\name\AppData\Local\Programs\Python\Python35-32\python.exe. Replace name with your Windows username. Depending on your installer and system, the Python directory can also be Python35-64. As mentioned earlier, at the time of installation, you should select the option Add Python 3.5 to PATH to make sure python or python.exe are automatically recognized as commands. Alternatively, you can rerun the installer with just this option checked.

Verifying Python installation

Open a terminal window (or command prompt on Windows OS) and type the following command to verify the Python version. This command will work if Python is installed and is available as a command in the terminal window. Otherwise, specify the full path to the Python executable. For instance, on Linux you can specify it as /usr/bin/python, if Python is installed in /usr/bin:

$ python -V

Tip

Note that the $ sign in the previous command line belongs to the terminal window and is not part of the command itself! Put another way, the actual command is just python -V. The $ or % sign in the terminal window is a prompt for a normal user on Linux. For a root (admin) user, the sign is #. Likewise, on Windows OS, the corresponding symbol is >. You will type the actual command after this symbol.

The following is just a sample output, if we run the preceding command:

[user@hostname ~]$ python -V
Python 3.5.1 :: Anaconda 4.0.0 (64-bit)

Installing pip

The pip is a software package manager that makes it trivial to install Python packages from the official third party software repository, PyPI. The pip is already installed for Python-2 version 2.7.9 or higher and Python-3 version 3.4 or higher. If you are using a different Python version, check out https://pip.pypa.io/en/stable/installing for the installation instructions.

On Linux OS, the default location for the pip is same as that of the Python executable. For example, if you have /usr/bin/python, then pip should be available as /usr/bin/pip. On Windows OS, the default pip.exe is typically the following: C:\Users\name\AppData\Local\Programs\Python\Python35-32\Scripts\pip.exe. As mentioned earlier, replace name with your Windows username. Depending on your installer and the system, the Python directory can also be Python35-64.

Installing IPython

This is an optional installation. IPython is an enhanced version of the Python interpreter. If it is not already bundled in your Python distribution, you can install it with:

$ pip install ipython

After the installation, just type ipython in the terminal to start the IPython interactive shell. Here is a screenshot of the IPython shell using the Anaconda Python 3.5 distribution:

Tip

It is often very convenient to use the Jupyter Notebook to write and share interactive programs. It is a web application that enables an interactive environment for writing Python code alongside rich text, images, plots, and so on. For further details, check out the project homepage at http://jupyter.org/. The Jupyter Notebook can be installed with:

$ pip install "ipython[notebook]"

Choosing an IDE

Using an IDE for development is a matter of personal preference. Simply put, an IDE is a tool intended to accelerate application development. It enables developers to write efficient code quickly by integrating the most common tools they need. The Python installation comes with a program called IDLE. It is a basic IDE for Python, which should get you started. For advanced development, you can choose from a number of freely or commercially available tools. Any good Python IDE has the following minimum features:

A source code editor with code completion and syntax highlighting features
A code browser to browse through files, projects, functions, and classes
A debugger to interactively identify problems
A version control system integration such as Git

You can get started by trying out one of the freely available IDEs. Here is a partial list of popular IDEs. If you are just interested in a simple source code editor, you can check out https://wiki.python.org/moin/PythonEditors, for a list of available choices.

Python IDE	Notes
PyCharm Community Edition https://www.jetbrains.com/pycharm	Has a free community edition. Excellent tool to begin Python development!
Wing IDE 101 http://wingware.com/downloads/wingide-101	Free for non-commercial purposes only. Commercial version available with additional features. Another excellent Python IDE.
Spyder https://pythonhosted.org/spyder	Freely available, open source. Also provided in bundled Python distributions such as Python(x,y) and Anaconda.
Eclipse PyDev www.pydev.org	Freely available, open source.
Sublime Text 2 or Sublime Text 3 (beta) http://www.sublimetext.com/2	Free for evaluation purposes only. Highly configurable IDE.

The theme of the book

Have you read high fantasy novels, such as The Lord of the Rings or The Hobbit by J. R. R. Tolkien? Or watched the films based on these novels? Well, here is a high fantasy, "Tolkienesque" themed book on Python application development.

Tip

To find out more about J.R.R. Tolkien's work, see https://en.wikipedia.org/wiki/J._R._R._Tolkien. The term high fantasy is often used to represent a fantasy theme set in an alternate fictional world. Check out https://en.wikipedia.org/wiki/High_fantasy for more information.

This book takes you to an imaginary world where you will develop a text game based on the aforementioned theme. Yes, you can continue being a developer even in this imaginary world! During the course of the book, you will be accompanied by many fictional characters. While you learn different aspects of Python development, these characters will talk to you, ask questions, request new features, and even fight with the enemy.

It should be noted that this book is not about developing game applications. It uses a simple text-based game just as a medium to learn various development aspects.

Tip

Off topic, if you are interested in playing a high fantasy theme game, there are quite a few to choose from. Among the open source ones, Battle for Wesnoth is one of the most highly rated, free, turn-based strategy games with a high fantasy theme. Check out https://www.wesnoth.org, for more details.

Meet the characters

Let's meet the imaginary characters who will accompany you in various chapters:

	Sir Foo A human knight who is portrayed as a grand knight guarding the southern plains. He is our main character and will be talking to us throughout the book.
	Orc Rider An Orc is a human-like imaginary creature. Here, it is portrayed as an enemy soldier. The Orc is seen riding a wild boar-like creature. You will see this creature in this chapter.
	Elf Rider An Elf is a supernatural mythical being. The Elf is mounted on an elvish horse. He is portrayed as a friendly. You will meet Mr. Elf in Chapter 6, Design Patterns.
	Fairy An intelligent fairy with an inherent capability for magic. She will use her magic just once while finding her enchanted locket in Chapter 7, Performance Identifying Bottlenecks, (See O(log n)). You will first meet her in Chapter 6, Design Patterns.
	Dwarf A Dwarf is a small human-like mythical being. He is portrayed as "The Great Dwarf" of the Foo mountains. He asks lots of questions. You will see him in the second half of the book, starting with Chapter 6, Design Patterns.

With this fun theme as a vehicle, let's start our journey with a simple command-line application. It will be a text-based game. The complexities added in subsequent chapters will challenge you with interesting problems. The book will show you how to gracefully handle such situations.

Key benefits

Get to grips with Python techniques that address commonly encountered problems in general application development.

Develop, package, and deploy efficient applications in a fun way.

All-practical coverage of the major areas of application development, including best practices, exception handling, testing, refactoring, design patterns, performance, and GUI application development.

Description

Python is one of the most widely used dynamic programming languages, supported by a rich set of libraries and frameworks that enable rapid development. But fast paced development often comes with its own baggage that could bring down the quality, performance, and extensibility of an application. This book will show you ways to handle such problems and write better Python applications. From the basics of simple command-line applications, develop your skills all the way to designing efficient and advanced Python apps. Guided by a light-hearted fantasy learning theme, overcome the real-world problems of complex Python development with practical solutions. Beginning with a focus on robustness, packaging, and releasing application code, you’ll move on to focus on improving application lifetime by making code extensible, reusable, and readable. Get to grips with Python refactoring, design patterns and best practices. Techniques to identify the bottlenecks and improve performance are covered in a series of chapters devoted to performance, before closing with a look at developing Python GUIs.

What you will learn

Build a robust application by handling exceptions.

Modularize, package, and release the source distribution.

Document the code and implement coding standards.

Create automated tests to catch bugs in the early development stage.

Identify and re-factor badly written code to improve application life.

Detect recurring problems in the code and apply design patterns.

Improve code efficiency by identifying performance bottlenecks and fixing them.

Develop simple GUI applications using Python.

What do you get with Print?

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Total € 115.97

Will Ware Oct 13, 2016

Disclosure: I am the technical reviewer for this book and I received a complimentary copy from the author. That said, I'm delighted with the book, and to have in some small way contributed to its excellence. While the fantasy game theme might suggest this is a book for beginners, it is densely packed with resources that will serve the needs of advanced Python developers. After two chapters of basics, Ninad moves on to creating and distributing packages, code documentation and quality monitoring, unit testing and mocking, refactoring, measuring and improving performance, and GUI programming. Each topic is a deep dive, examining multiple approaches and making informed recommendations, far beyond the casual web searching that software developers (myself included) routinely do in our haste to accomplish specific goals. I look forward to using the book in my daily work and plan to recommend it to friends and co-workers. After ten-plus years of professional Python development, I fully expect that working with this book will improve the quality of my output.

Amazon Verified review

Qi Feb 11, 2019

I bought the Chinese translation version of this book a year ago and read less than 2 chapters after I bought it. I started to read it again since yesterday and spent a day and finished 6 chapters and found it’s very helpful for me to better understand not only python as a language but also many aspects for software development. Many concepts were introduced in a simple way and easily connected with actual corresponding code.

Learning Python Application Development: Take Python beyond scripting to build robust, reusable, and efficient applications

What do you get with Print?

Learning Python Application Development

Chapter 1. Developing Simple Applications

Important housekeeping notes

Installation prerequisites

Tip

Installing Python

Option 1 – official distribution

Option 2 – bundled distribution

Python install location

Tip

Unix-like operating systems

Windows OS

Verifying Python installation

Tip

Installing pip

Installing IPython

Tip

Choosing an IDE

The theme of the book

Tip

Tip

Meet the characters

Page 1 of 9

Key benefits

Description

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What you will learn

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Learning Python Application Development: Take Python beyond scripting to build robust, reusable, and efficient applications

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Contact Details

Shipping Address

Billing Address

Option 1 – official distribution

Option 2 – bundled distribution

Python install location

Unix-like operating systems

Windows OS

Verifying Python installation

Installing pip

Installing IPython

Choosing an IDE

Key benefits

Description

Who is this book for?

What you will learn

Product Details

What do you get with Print?

Contact Details

Shipping Address

Billing Address

Product Details

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Frequently bought together

Table of Contents

Recommendations for you

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