Setup a Proper Python Environment

Python is available on a wide range of platforms, including Linux and Mac OS X. We are trying to figure out how to create our Python environment.

Configuring your local environment

Open the terminal window and type “python” to check if it is already installed and what version is installed.

• Unix (Solaris, Linux, FreeBSD, AIX, HP/UX, SunOS, IRIX, etc.)
• Win 9x/NT/2000
• Macintosh (Intel, PPC, 68K)
• OS/2
• DOS (multiple versions)
• PalmOS
• Nokia mobile phones
• Windows CE
• Acorn/RISC OS
• BeOS
• Amiga
• VMS/OpenVMS
• QNX
• VxWorks
• Psion
• Python has also been ported to the Java and .NET virtual machines

Get Python

The latest and most up-to-date source code, binaries, documentation, news, etc. are available on the official Python website https://www.python.org/.

Python documentation can be downloaded from https://www.python.org/doc/. Documentation is available in HTML, PDF and PostScript formats.

Python Installation

Python distribution is available for many different platforms. Just download the right binary code for your platform and install Python.

If the binary code for your platform is not available, you need the C compiler to compile the source code manually. Compiling the source code gives you more flexibility in choosing the features you need for your installation.

Here is a brief summary of Python installations on different platforms –

Installing Unix and Linux

Here are a few simple steps to install Python on a Unix/Linux machine

This installs Python in the standard /usr/local/bin location and its library in /usr/local/lib/pythonXX where XX is the Python version.

Windows Installation

Here are the steps to install Python on your Windows computer.

– Open your Internet browser and go to https://www.python.org/downloads/.

– Click on the link to the Windows Python-XYZ.msi installation file, where XYZ is the version you need to install.

– To use this Python-XYZ.msi installer, Windows must support Microsoft Installer 2.0. Save the installation file to your local computer, and then run it to see if your computer supports MSI.

– Run the downloaded file. This will launch the Python installation wizard, which is very easy to use. Simply accept the default settings, wait until the installation is complete, and you’re done.

Install on Macintosh

The latest Macs have Python installed, but it may be several years old. See http://www.python.org/download/mac/ for instructions on how to get the current version with additional development tools on your Mac. For operating systems prior to Mac OS X 10.3 (released in 2003), MacPython is available.

Jack Jansen maintains it, and full access to all documentation is available at his website – http://www.cwi.nl/~jack/macpython.html. Full details of the Mac OS installation can be found on the website.

Setting up PATH

Programs and other executable files can be in many directories, so operating systems provide a search path that lists the directories where the operating system searches for executables.

The path is stored in an environment variable, which is a name string maintained by the operating system. This variable contains information available for the command shell and other programs.

The path variable is called PATH on Unix or Path on Windows (Unix is case sensitive; Windows is not).

On Mac OS, the installer handles the path details. To call the Python interpreter from a particular directory, you must add the Python directory to your path.

Setting path at Unix/Linux

To add the Python directory to the path for a particular session in Unix −

• In the csh shell − type setenv PATH “$PATH:/usr/local/bin/python” and press Enter.
• In the bash shell (Linux) − type export PATH=”$PATH:/usr/local/bin/python” and press Enter.
• In the sh or ksh shell − type PATH=”$PATH:/usr/local/bin/python” and press Enter.
• Note − /usr/local/bin/python is the path of the Python directory

Setting path at Windows

To add the Python directory to the path for a particular session in Windows −

At the command prompt − type path %path%;C:\Python and press Enter.

Note − C:\Python is the path of the Python directory

Python Environment Variables

Here are important environment variables, which can be recognized by Python −

Sr.No.	Variable & Description
1	PYTHONPATH It has a role similar to PATH. This variable tells the Python interpreter where to locate the module files imported into a program. It should include the Python source library directory and the directories containing Python source code. PYTHONPATH is sometimes preset by the Python installer.
2	PYTHONSTARTUP It contains the path of an initialization file containing Python source code. It is executed every time you start the interpreter. It is named as .pythonrc.py in Unix and it contains commands that load utilities or modify PYTHONPATH.
3	PYTHONCASEOK It is used in Windows to instruct Python to find the first case-insensitive match in an import statement. Set this variable to any value to activate it.
4	PYTHONHOME It is an alternative module search path. It is usually embedded in the PYTHONSTARTUP or PYTHONPATH directories to make switching module libraries easy.

Running Python

There are three different ways to start Python −

Interactive Interpreter

You can start Python from Unix, DOS, or any other system that provides you a command-line interpreter or shell window.

Enter python the command line.

Start coding right away in the interactive interpreter.

$python # Unix/Linux

or

python% # Unix/Linux

or

C:> python # Windows/DOS

Here is the list of all the available command line options −

Sr.No.	Option & Description
1	-d It provides debug output.
2	-O It generates optimized bytecode (resulting in .pyo files).
3	-S Do not run import site to look for Python paths on startup.
4	-v verbose output (detailed trace on import statements).
5	-X disable class-based built-in exceptions (just use strings); obsolete starting with version 1.6.
6	-c cmd run Python script sent in as cmd string
7	file run Python script from given file

Script from the Command-line

A Python script can be executed at command line by invoking the interpreter on your application, as in the following −

$python script.py # Unix/Linux

or

python% script.py # Unix/Linux

or

C: >python script.py # Windows/DOS

Note − Be sure the file permission mode allows execution.

Integrated Development Environment

You can run Python from a Graphical User Interface (GUI) environment as well, if you have a GUI application on your system that supports Python.

• Unix − IDLE is the very first Unix IDE for Python.
• Windows − PythonWin is the first Windows interface for Python and is an IDE with a GUI.
• Macintosh − The Macintosh version of Python along with the IDLE IDE is available from the main website, downloadable as either MacBinary or BinHex’d files.

If you are not able to set up the environment properly, then you can take help from your system admin. Make sure the Python environment is properly set up and working perfectly fine.

Note − All the examples given in subsequent chapters are executed with Python 3.0 version available on CentOS flavor of Linux.

We already have set up Python Programming environment online, so that you can execute all the available examples online at the same time when you are learning theory. Feel free to modify any example and execute it online.