CHAPTER 2 | Python Environment

Python Environment

Before we start writing our Python programs, let's understand how to set up our Python environment.

Python is available on a wide variety of platforms including Linux and Mac OS X. Try opening a terminal window and type "python" to find out if its already installed and which version you have if it 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

VxWorks

Psion

Python has also been ported to the Java and .NET virtual machines

Getting Python:

The most up-to-date and current source code, binaries, documentation, news, etc. is available at the official website of Python:

Python Official Website : http://www.python.org/

You can download Python documentation from the following site. The documentation is available in HTML, PDF and PostScript formats.

Python Documentation Website : www.python.org/doc/

Install Python:

Python distribution is available for a wide variety of platforms. You need to download only the binary code applicable for your platform and install Python.

If the binary code for your platform is not available, you need a C compiler to compile the source code manually. Compiling the source code offers more flexibility in terms of choice of features that you require in your installation.

Here is a quick overview of installing Python on various platforms:

Unix & Linux Installation:

Here are the simple steps to install Python on Unix/Linux machine.

Open a Web browser and go to http://www.python.org/download/

Follow the link to download zipped source code available for Unix/Linux.

Download and extract files.

Editing the Modules/Setup file if you want to customize some options.

run ./configure script

make

make install

This will install python in a standard location /usr/local/bin and its libraries are installed in/usr/local/lib/pythonXX where XX is the version of Python that you are using.

Windows Installation:

Here are the steps to install Python on Windows machine.

Open a Web browser and go to http://www.python.org/download/

Follow the link for the Windows installer python-XYZ.msi file where XYZ is the version you are going to install.

To use this installer python-XYZ.msi, the Windows system must support Microsoft Installer 2.0. Just save the installer file to your local machine and then run it to find out if your machine supports MSI.

Run the downloaded file by double-clicking it in Windows Explorer. This brings up the Python install wizard, which is really easy to use. Just accept the default settings, wait until the install is finished, and you're ready to roll!

Macintosh Installation:

Recent Macs come with Python installed, but it may be several years out of date. See http://www.python.org/download/mac/ for instructions on getting the current version along with extra tools to support development on the Mac. For older Mac OS's before Mac OS X 10.3 (released in 2003), MacPython is available."

Jack Jansen maintains it and you can have full access to the entire documentation at his Web site - Jack Jansen Website : http://www.cwi.nl/~jack/macpython.html

Just go to this link and you will find complete installation detail for Mac OS installation.

Setting up PATH:

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

The path is stored in an environment variable, which is a named string maintained by the operating system. These variables contain information available to the command shell and other programs.

The path variable is named PATH in Unix or Path in Windows (Unix is case-sensitive; Windows is not).

In Mac OS, the installer handles the path details. To invoke the Python interpreter from any 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:

Running Python:

There are three different ways to start Python:

(1) Interactive Interpreter:

You can enter python and start coding right away in the interactive interpreter by starting it from the command line. You can do this from Unix, DOS or any other system, which provides you a command-line interpreter or shell window.

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

(2) 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:

Note: Be sure the file permission mode allows execution.

(3) Integrated Development Environment

You can run Python from a graphical user interface (GUI) environment as well. All you need is 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.

Before proceeding to next chapter, make sure your environment is properly set up and working perfectly fine. If you are not able to set up the environment properly, then you can take help from your system admin.

All the examples given in subsequent chapters have been executed with Python 2.4.3 version available on CentOS flavor of Linux.

About MANI KUMAR CHOWDARY

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