Python is available on a wide variety of platforms including Linux and Mac OS X.
Local Environment Setup
The most up-to-date and current source code, binaries, documentation, news, etc., is available on the official website of Python: http://www.python.org/.
You can download Python documentation from www.python.org/doc/. The documentation is available in HTML, PDF, and PostScript formats.
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.
Unix and 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
This installs Python at standard location /usr/local/bin and its libraries at /usr/local/lib/pythonXX where XX is the version of Python.
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 need to install.
To use this installer python-XYZ.msi, the Windows system must support Microsoft Installer 2.0. Save the installer file to your local machine and then run it to find out if your machine supports MSI.
Run the downloaded file. 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 are done.
Recent Macs come with Python installed, but it may be several years out of date.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
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 website - http://www.cwi.nl/~jack/macpython.html. You can find complete installation details for Mac OS installation.
Setting up PATH
Programs and other executable files can be 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. This variable contains information available to the command shell and other programs.
The path variable is named as 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 "$PATH:/usr/local/bin/python" and press Enter.
In the bash shell (Linux): type export ATH="$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 director
Linux Python Environment Variables
Here are important environment variables, which can be recognized by Python:
|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.|
|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|
|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.|
|PYTHONHOME||It is an alternative module search path. It is usually|
|embedded in the PYTHONSTARTUP or PYTHONPATH|
|directories to make switching module libraries easy.|
There are three different ways to start Python:
(1) 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.
$python # Unix/Linux
python% # Unix/
C:>python # Windows/DOS
Here is the list of all the available command line options:
|-d||It provides debug output.|
|-O||It generates optimized bytecode (resulting in .pyo files).|
|-S||Do not run import site to look for Python paths on startup.|
|-v||verbose output (detailed trace on import statements).|
|-X||disable class-based built-in exceptions (just use strings); obsolete|
|starting with version 1.6.|
|-c cmd||run Python script sent in as cmd string|
|file||run Python script from given file|
(2) Script from the Command-line
A Python script can be executed at command line by invoking the interpreter on your application
|$python script.py||# Unix/Linuxor|
|python% script.py||# Unix/Linuxor||C:>python script.py||#|
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, if you have a GUI application on your system that supports Python.
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.
Windows: PythonWin is the first Windows interface for Python and is an IDE with a GUI.
Make sure the Python environment is properly set up and working perfectly fine.The Python language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages.
First Python Program
Let us execute programs in different modes of programming.
Interactive Mode Programming:
Invoking the interpreter without passing a script file as a parameter brings up the following prompt:
Python 2.4.3 (#1, Nov 11 2010, 13:34:43)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
Type the following text at the Python prompt and press the Enter:
>>> print "Hello, Python!";
If you are running new version of Python, then you need to use print statement with parenthesis as in print ("Hello, Python!");. However in Python version 2.4.3, this produces the following result:
Script Mode Programming
Invoking the interpreter with a script parameter begins execution of the script and continues until the script is finished. When the script is finished, the interpreter is no longer active.
Let us write a simple Python program in a script. Python files have extension .py. Type the following source code in a test.py file:
print "Hello, Python!";
We assume that you have Python interpreter set in PATH variable. Now, try to run this program as follows:
$ python test.py
This produces the following result:
Let us try another way to execute a Python script. Here is the modified test.py file:
print "Hello, Python!";
We assume that you have Python interpreter available in /usr/bin directory. Now, try to run this program as follows:
$ chmod +x test.py # This is to make file executable
This produces the following result: