handout_3b.txt

CS 35L Software Construction Laboratory (Lab3-B)
Wed, April 18, 2012, Ver 1.2

Python Reading: 
    http://docs.python.org/release/2.4.1/tut/tut.html
    Ch1 ~ Ch7: must read, read the rest if you want more powerful tools
    http://learnpythonthehardway.org
    Lots of small exercises, very helpful

Python in Interactive mode
  Simply type "python" in the command line
  -- It is a good calculator
       e.g. >>> import math
            >>> math.sqrt ((3 + 4.5) ** 2)
            7.5 
  -- It is a good helper for pyhton
       e.g. >>> help(open)

Revisit: Run a (Python) script
  Option 1: python myscript.py
  Option 2: #! line and chomd +x

Indent is important in Python
  something is wrong with the following code
  ----------------------------------------
  def test():
      x = 0
    for i in range(0, 10):
      x += i
       print x
    test()
  ----------------------------------------

Python variables
  Strong typed
  Dynamically, implicitly typed
  ----------------------------------------
  >>> a = '1'
  >>> type(a)
  <type 'str'>
  >>> 2 + a
  type error!
  ----------------------------------------
  >>> a = 1
  >>> type(a)
  <type 'int'>
  ----------------------------------------
  Every variable is an instace of object.
  >>> a = dict   #type object
  >>> a = dict() #a new instance of dict()
  >>> a = len    #function objec
  ----------------------------------------

Build-in Data Structure in Python
  -- Basic type: int, float
  -- Tuple: immutable, (generally) sequences of different kinds of stuff
  -- List: mutable, (generally) sequences of the same kind of stuff
     Ref: http://news.e-scribe.com/397
  -- String: 'string', "string", """string"""
       Acutally, there is no character type in Python
       >>> type('a')
       <type 'str'>
  -- Access tuple, list and string using subscriptions
     a[1], a[1:], c[2:4], a[-1], a[:-1]
  -- Dict: key, value pairs
     e.g. d = {}
          d["tom"] = 20
          d["jerry"] = 19
     d.values(), d.keys(), d.items()

The main function in Python
  ----------------------------------------
  #! /usr/bin/env python

  def main():
    print 'hello world'

  if __name__ == "__main__":
    main()
  ----------------------------------------

    This line indicates the entry point of the program. If we don't specify
  this line, it will execute from the first "module-level" statement.

  Best practice:
    Always enclose your code in a function, use a main function if you want
 to execute from the script directly.

  -- Arguments --
    The command line arguments can be accessed
  using sys.argv. sys.argv is a list, the arguments
  will be listed in their original order starting
  from sys.argv[1] (sys.argv[0] is the script name).