Configuring Debian for Python Web Development¶

Note: the following instructions assume that you are connected to the Internet and that you have the standard Debian package repositories enabled. All unix shell commands are assumed to be running from your home directory ($HOME). Finally, any command that begins with sudo assumes that you have administrative rights on your machine. If you do not — please ask your system administrator about installing the software you need.

What follows are instructions for setting up an Debian 12 (bookworm) home environment for use with this book. I use Debian for both development and testing of the book, so it is the only system about which I can personally answer setup and configuration questions.

In the spirit of software freedom and open collaboration, please contact me if you would like to maintain a similar appendix for your own favorite system. I’d be more than happy to link to it or put it on the Open Book Project site, provided you agree to answer user feedback concerning it.

Thanks!

Jeffrey Elkner

Arlington, Virginia

Python3¶

While Debian bookworm only comes with Python 3 installed, the legacy of Python 2 is still with us. Typing python at the shell prompt will give a command not found error.

Use the command python3 for Python 3.

Note: You can fix this behavior by installing the python-is-python3 package with:

$ sudo apt install python-is-python3

The book examples assume you have done this.

In addition to the debian packages in the Debian package archive, we will be using Python software from the Python Package Index or PyPI. The tool for installing packages from PyPI is called pip.

To add this package run following from the unix command prompt:

$ sudo apt install python3-pip

Now would also be a good time to install a few other packages you will want to have on your system:

$ sudo apt install python3-tk pycodestyle git

This will install the Tkinter GUI toolkit, the pep8 Python style checker, and the git revision control system which we will use to grab some program examples.

Bottle¶

Bottle is a micro web application framework written in Python. It is used in this book to introduce web application development.

To install bottle run:

$ sudo apt install python3-bottle

Then try:

>>> import bottle

at the python prompt to varify that it is working.

Vim¶

Vim can be used very effectively for Python development, but Ubuntu only comes with the vim-tiny package installed by default, so it doesn’t support color syntax highlighting or auto-indenting.

To use Vim, do the following:

From the unix command prompt, run:
```
$ sudo apt install vim
```

Create a file in your home directory named .vimrc that contains the following:

syntax enable
filetype indent on
set et
set sw=4
set smarttab
map <f3> :w\|!python % <cr>
map <f4> :w\|!python -m doctest -v % <cr>
map <f8> :w\|!pycodestyle % -v <cr>

When you edit a file with a .py extension, you should now have color systax highlighting and auto indenting. Pressing the <f3> key should run your program, and bring you back to the editor when the program completes. <f4> runs the program with the verbose (-v) switch set, which will be helpful when running doctests. <f8> will run the pep8 style checker against your program source, which is useful in helping you learn to write Python programs with good styling.

To learn to use vim, run the following command at a unix command prompt:

$ vimtutor

$HOME environment¶

The following creates a useful environment in your home directory for using pip3 to install packages into your home directory and for adding your own Python libraries and executable scripts:

From the command prompt in your home directory, create bin and lib subdirectories of your .local directory by running the following command:
```
$ mkdir .local/lib .local/bin
```
Now add a my_python subdirectory to .local/lib:
```
$ mkdir .local/lib/my_python
```
Add the following lines to the bottom of your .bashrc in your home directory:
```
EDITOR=vim
PATH=$HOME/.local/bin$PATH
PYTHONPATH=$HOME/.local/lib/my_python

export EDITOR PATH PYTHONPATH
```
This will set your prefered editor to Vim, add your own .local/bin directory as a place to put executable scripts, and add .local/lib/my_python to your Python search path so modules you put there will be found by Python.

Then run:
```
$ . .bashrc
```
to set these environment varialbles and prepend the .local/bin directory to your search path (note: logging out and back in will accomplish the same result).

Lumpy¶

Lumpy is python module that generates UML diagrams. It was written by Allen B. Downey as part of his Swampy suite of Python programs written for use with his textbooks.

The version here is modified to work with Python 3 on Ubuntu 16.04. Click on lumpy.py to download the module. Put this file in your .local/lib/my_python directory after your $HOME environment is configured.

Lumpy is used in several of the exercises in this book to help illustrate python data structures.

Making a python script executable and runnable from anywhere¶

On unix systems, Python scripts can be made executable using the following process:

Add this line as the first line in the script:
```
#!/usr/bin/env python3
```
At the unix command prompt, type the following to make myscript.py executable:
```
$ chmod +x myscript.py
```
Move myscript.py into your .local/bin directory, and it will be runnable from anywhere.