Short introduction to Python 3.2 (Spring 2012):
(2.X may be slightly different)
References:

Getting started:
New scripts:
  1. Open IDLE (Python Developement tool)  (On windows: from the "Start Menu") .  This opens a "Python Shell" window.
  2. Pull down the File menu and click on "New Window".  This opens the editor.
  3. In the "Edit Window", save the empty text in a file with an extension .py.   This will format your script as you type.
  4. To run the script from the "Edit Window", pull down the "Run" menu  and click on "Run Module.  The script will execute t in the "Python Shell" window.
Existing scripts:
    1. Right click on file and select "Edit with Idle".
There a many other ways to edit and run Python, including not using IDLE.

Some important language features:
  1. Multi-paradigm language
    1. Object orientation, structured programming, functional programming, aspect-oriented programming, and more recently, design by contract are all supported.
  2. dynamically typed 
    1. -- no declaration of variables
    2. -- type "lives" with objects, not names
  3. OO and functional
  4. reference model like Java
  5. Layout rule: White spaces delimit blocks of code instead of symbols like "{}" in C or keywords like begin and end in Pascal.
    1. IDLE will automatically format according to the layout rule.
  6. Notice the use of ":" in for, while, def and if statements.
  7. and -- logical and operator
    not -- logical negation operator
  8. elif can be used for "optional parts"
    9. if n < 5:
        return 10
    elif n < 20:
        return 100
    else:
        return 1000
Example code:
fib.py

# Recursive definition of  the nth fibonacci number

def fib (n):
    if n < 2:
        return 1
    else :
        return fib(n-1) + fib (n-2)

# Iterative definition

def fibi (n):
     a = 1
     b = 1
     s = 1
     while s < n:
         s += 1
         t = a + b
         a = b
         b = t
     return b

# using for loop

def fibf (n):
    a = 1
    b = 1
    for i in range (2,n+1):    # i assumes the values 2 to n
        t = a + b
        a = b
        b = t
    return b