Python

python tutorial pdf

python tutorial pdf, Python is a high-level, interpreted, interactive, and object-oriented scripting language. Python is designed to be highly readable.  It uses  English keywords frequently whereas other languages use punctuation, and it has fewer syntactical constructions than other languages.

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Python ─

Python is a high-level, interpreted, interactive, and object-oriented scripting language. Python is designed to be highly readable.  It uses  English keywords frequently whereas other languages use punctuation, and it has fewer syntactical constructions than other languages.

  • Python is Interpreted: Python is processed at runtime by the interpreter. You do not need to compile your program before executing it. This is similar to PERL and PHP.
  • Python is Interactive: You can actually sit at a Python prompt and interact with the interpreter directly to write your programs.
  • Python is Object-Oriented: Python supports an Object-Oriented style or technique of programming that encapsulates code within objects.
  • Python is a Beginner’s Language: Python is a great language for beginner-level programmers and supports the development of a  wide range of applications from simple text processing to WWW browsers to games.

History of Python:

Python was developed by Guido van Rossum in the late eighties and early nineties at the National Research Institute for Mathematics and Computer Science in the Netherlands.

Python is derived from many other languages, including ABC, Modula-3, C, C++, Algol-68, SmallTalk, Unix shell, and other scripting languages.

Python is copyrighted. Like Perl, Python source code is now available under the GNU General Public License (GPL).

Python is now maintained by a core development team at the institute, although Guido van Rossum still holds a vital role in directing its progress.

Python Features

Python’s features include:

  • Easy-to-learn: Python has few keywords, a simple structure,  and a  clearly defined syntax. This allows the student to pick up the language quickly.
  • Easy-to-read: Python code is more clearly defined and visible to the eyes.
  • Easy-to-maintain: Python’s source code is fairly easy-to-maintain.
  • A broad standard library: Python’s bulk of the library is very portable and cross-platform compatible on UNIX, Windows, and Macintosh.
  • Interactive  Mode: Python has support for an interactive mode that allows interactive testing and debugging of snippets of code.
  • Portable: Python can run on a wide variety of hardware platforms and has the same interface on all platforms.
  • Extendable: You can add low-level modules to the Python interpreter. These modules enable programmers to add to or customize their tools to be more efficient.
  • Databases: Python provides interfaces to all major commercial databases.
  • GUI Programming: Python supports GUI applications that can be created and ported to many system calls,  libraries,  and windows systems,  such as  Windows  MFC, Macintosh, and the X Window system of Unix.
  • Scalable: Python provides a better structure and support for large programs than shell scripting.

Apart from the above-mentioned features, Python has a big list of good features, few are listed below:

  • It supports functional and structured programming methods as well as OOP.
  • It can be used as a scripting language or can be compiled to byte-code for building large applications.
  • It provides very high-level dynamic data types and supports dynamic type checking.
  • It supports automatic garbage collection.
  • It can be easily integrated with C, C++, COM, ActiveX, CORBA, and Java.

Python is available on a  wide variety of platforms including  Linux and  Mac  OS  X.  Let’s understand how to set up our Python environment.

LocalEnvironmentSetup

Open a terminal window and type “python” to find out if it is already installed and which 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

Getting Python

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.

Installing Python

Python distribution is available for a wide variety of platforms. You need to download only the binary code applicable to 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 the choice of features that you require in your installation.

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

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 the 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 installs Python at standard location /usr/local/bin and its libraries at /usr/local/lib/pythonXX where XX is the version of Python.

Windows Installation

Here are the steps to install Python on a 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.

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 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.

SettingpathatUnix/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

The 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

PythonEnvironmentVariables:

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

Variable Description
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 PYTHONPATH.
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.

 

RunningPython

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

or

python%             # Unix/Linux or

C:>python           # Windows/DOS

 

 

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

Option Description
-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 the command  line  by  invoking  the  interpreter  on  your application, as in the following:

Note: Be sure the file permission mode allows execution.

$python script.py # Unix/Linux or
python% script.py # Unix/Linux or   C:>python script.py # Windows/DOS

(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.

  • 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 2.4.3 version available on CentOS flavor of Linux.

We already have set up a 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

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