=====================
Basic Python Workshop
=====================

This document is intended to be handed out at the end of the workshop. It has
been designed for Engineering students who are Python beginners and have basic
programming skills. The focus is on basic numerics and plotting using Python.

The system requirements:
  * Python - version 2.5.x or newer.
  * IPython 
  * Text editor - scite, vim, emacs or whatever you are comfortable with.

1. Introduction
===============

The Python programming language was created by a dutch named Guido van Rossum.
The idea of Python was conceived in December 1989. The name Python has nothing
to do with the reptilian, but its been named after the 70s comedy series 
"Monty Python's Flying Circus", since it happens to be Guido's favourite 
TV series. 

Current stable version of Python is 2.6.x, although Python 3.0 is also the stable
version, it is not backwards compatible with the previous versions and is hence
not entirely popular at the moment. This material will focus on the 2.6.x series.
  
Python is licensed under the Python Software Foundation License (PSF License) 
which is GPL compatible Free Software license (excepting license version 1.6 and 2.0)
It is a no strings attached license, which means the source code is free to modify
and redistribute.

The Python docs define Python as "Python is an interpreted, object-oriented, 
high-level programming language with dynamic semantics." A more detailed summary
can be found at http://www.python.org/doc/essays/blurb.html. Python is a language that
has been designed to help the programmer concentrate on solving the problem at hand
and not worry about the programming language idiosyncrasies.

Python is a highly cross platform compatible language on account of it being an 
interpreted language. It is highly scalable and hence has been adapted to run on 
the Nokia 60 series phones. Python has been designed to be readable and easy to use

**Resources available for reference**

* Web: http://www.python.org
* Doc: http://www.python.org/doc
* Free Tutorials:
    * Official Python Tutorial: http://docs.python.org/tut/tut.html
    * Byte of Python: http://www.byteofpython.info/
    * Dive into Python: http://diveintopython.org/

**Advantages of Python - Why Python??**

* Python has been designed for readability and ease of use. Its been designed in 
  such a fashion that it imposes readability on the programmer. Python does away
  with the braces and the semicolons and instead implements code blocks based on 
  indentation, thus enhancing readability. 

* Python is a high level, interpreted, modular and object oriented language.
  Python performs memory management on its own, thus the programmer need not bother
  about allocating and deallocating memory to variables. Python provides extensibility
  by providing modules which can be easily imported similar to headers in C and 
  packages in Java. Python is object oriented and hence provides all the object oriented
  characteristics such as inheritance, encapsulation and polymorphism.

* Python offers a highly powerful interactive programming interface in the form
  of the 'Interactive Interpreter' which will be discussed in more detail in the 
  following sections.

* Python provides a rich standard library and an extensive set of modules. The 
  power of Python modules can be seen in this slightly exaggerated cartoon
  http://xkcd.com/353/

* Python interfaces well with most other programming languages such as C, C++ 
  and FORTRAN.

Although, Python has one setback. Python is not fast as some of the compiled 
languages like C or C++. Yet, the amount of flexibility and power more than make
up for this setback.


1.1 The Python Interpreter
--------------------------

1.1.1 The Interactive Interpreter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Typing *python* at the shell prompt on any standard Unix/Gnu-Linux system and
hitting the enter key fires up the Python 'Interactive Interpreter'. The Python
interpreter is one of the most integral features of Python. The prompt obtained
when the interactive interpreter is similar to what is shown below. The exact
appearance might differ based on the version of Python being used. The ``>>>``
thing shown is the python prompt. When something is typed at the prompt and the
enter key is hit, the python interpreter interprets the command entered and
performs the appropriate action.

::

  Python 2.5.2 (r252:60911, Oct  5 2008, 19:24:49) 
  [GCC 4.3.2] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  >>> 

Lets try with an example, type ``print 'Hello, World!'`` at the prompt and hit
the enter key. 

::

  >>> print 'Hello, World!'
  Hello, World!

This example was quite straight forward, and thus we have written our first
line of Python code. Now let us try typing something arbitrary at the prompt.
For example: 

::
  
  >>> arbit word
    File "<stdin>", line 1
      arbit word
              ^
  SyntaxError: invalid syntax
  >>>
    
The interpreter gave an error message saying that 'arbit word' was invalid
syntax which is valid. The interpreter is an amazing tool when learning to
program in Python. The interpreter provides a help function that provides the
necessary documentation regarding all Python syntax, constructs, modules and
objects. Typing *help()* at the prompt gives the following output:

::
  
  >>> help()
  
  Welcome to Python 2.5!  This is the online help utility.
  
  If this is your first time using Python, you should definitely check out
  the tutorial on the Internet at http://www.python.org/doc/tut/.
  
  Enter the name of any module, keyword, or topic to get help on writing
  Python programs and using Python modules.  To quit this help utility and
  return to the interpreter, just type "quit".
  
  To get a list of available modules, keywords, or topics, type "modules",
  "keywords", or "topics".  Each module also comes with a one-line summary
  of what it does; to list the modules whose summaries contain a given word
  such as "spam", type "modules spam".
  
  help> 
  

As mentioned in the output, entering the name of any module, keyword or topic
will provide the documentation and help regarding the same through the online
help utility. Pressing *Ctrl+d* exits the help prompt and returns to the
python prompt. 

Let us now try a few examples at the python interpreter. 

Eg 1:
::
  
  >>> print 'Hello, python!'
  Hello, python!
  >>>
  
Eg 2:
::
  
  >>> print 4321*567890
  2453852690
  >>> 
  
Eg 3:
::
  
  >>> 4321*567890
  2453852690L
  >>>

::
  
  Note: Notice the 'L' at the end of the output. The 'L' signifies that the
  output of the operation is of type *long*. It was absent in the previous
  example because we used the print statement. This is because *print* formats
  the output before displaying.
  
Eg 4:
::
  
  >>> big = 12345678901234567890 ** 3
  >>> print big
  1881676372353657772490265749424677022198701224860897069000
  >>> 

::
  
  This example is to show that unlike in C or C++ there is no limit on the
  value of an integer.

1.1.2 *ipython* - An enhanced interactive Python interpreter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The power and the importance of the interactive interpreter was the highlight
of the previous section. This section provides insight into the enhanced
interpreter with more advanced set of features called **ipython**. Entering
*ipython* at the shell prompt fires up the interactive interpreter. 

::
  
  $ ipython
  Python 2.5.2 (r252:60911, Oct  5 2008, 19:24:49) 
  Type "copyright", "credits" or "license" for more information.
  
  IPython 0.8.4 -- An enhanced Interactive Python.
  ?         -> Introduction and overview of IPython's features.
  %quickref -> Quick reference.
  help      -> Python's own help system.
  object?   -> Details about 'object'. ?object also works, ?? prints more.
  
  In [1]: 
  
This is the output obtained upon firing ipython. The exact appearance may
change based on the Python version installed. The following are some of the
various features provided by **ipython**:
  
  * Suggestions - ipython provides suggestions of the possible methods and
    operations available for the given python object.

Eg:
  
::
  
  In [4]: a = 6
  
  In [5]: a.
  a.__abs__           a.__divmod__        a.__index__         a.__neg__       
    a.__rand__          a.__rmod__          a.__rxor__
  a.__add__           a.__doc__           a.__init__          a.__new__       
    a.__rdiv__          a.__rmul__          a.__setattr__
  a.__and__           a.__float__         a.__int__           a.__nonzero__   
    a.__rdivmod__       a.__ror__           a.__str__
  a.__class__         a.__floordiv__      a.__invert__        a.__oct__       
    a.__reduce__        a.__rpow__          a.__sub__
  a.__cmp__           a.__getattribute__  a.__long__          a.__or__        
    a.__reduce_ex__     a.__rrshift__       a.__truediv__
  a.__coerce__        a.__getnewargs__    a.__lshift__        a.__pos__      
    a.__repr__          a.__rshift__        a.__xor__
  a.__delattr__       a.__hash__          a.__mod__           a.__pow__      
    a.__rfloordiv__     a.__rsub__          
  a.__div__           a.__hex__           a.__mul__           a.__radd__     
    a.__rlshift__       a.__rtruediv__      

In this example, we initialized 'a' (a variable - a concept that will be
discussed in the subsequent sections.) to 6. In the next line when the *tab* key
is pressed after typing '*a.*' ipython displays the set of all possible methods
that are applicable on the object 'a' (an integer in this context). Ipython
provides many such datatype specific features which will be presented in the
further sections as and when the datatypes are introduced.

1.2 Editing and running a python file
-------------------------------------

The