python.txt
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Python language: ecosystem

 Used for -- 
  CS education (this course!)  
  Application scripting (GIS, GNU Radio, ...)
  Systems administration and "glue"
  Web applications (Django etc. etc. etc.)
  Scientific/technical computing (a la MATLAB, Mathematica, also BioPython etc. ..)
  Software tools (automated software testing, distributed version control, ...)
  Research (natural language, graph theory, distributed computing, ...)

 An unusually large number of niches -- versatile

 Used by --
  Beginners
  Professional software developers, computer system administrators, ...  
  Professionals OTHER THAN computer specialists: biologists, urban planners, ....

 It is unusual for the same language to be popular among all these -- versatile
   
 You can be productive in Python WITHOUT full-time immersion!






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Python Language: features
 
 Gets many things right --
  Readable - looks nice, makes sense, usually matches expectations, intuitions
  No ideology about best way to program: 
   object-oriented programming,  functional, etc. all supported, but optional
  No platform preference - works as well in Windows, Mac, Linux, ...
  Easy to connect to other languages - C, Fortran - essential for science/math 
  Countless conveniences, large and small, make it pleasant to work with

 Features
  Unlike C, C++, C#, Java ... More like Ruby, Lisp, Perl, Matlab, Mathematica ...
  Dynamic - no type declarations - programs are shorter
  Interpreted - no separate compile, build steps - programming process is simpler

 Versions
  This class uses Python 2.x not Python 3 -- usually 2.6, 2.7, earlier would work

 Interpreter implementations
  I use CPython from python.org. Jython (JVM), Iron Python (.NET), PyPy also work






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How to write and run a Python program

   0. Maybe you don't need a program at all - just start Python and type ad lib

   $ python 
   >>> print 'Hello, world!' 
   Hello, world!

   module - a file that contains Python code, filename ends with .py
   Create module hello.py that contains: print 'Hello, world!'  Then ---
 
   1. python hello.py  # must be in current working directory

   2. python -m hello  # any module on PYTHONPATH anywhere on the system

   3. hello.py         # associate .py extension with python command (Windows)

   4. hello            # put #!/usr/env/python at top of module
   
   5. python
   >>> import hello    # importing a module executes its contents

   6. python -i hello.py  # import module, remain in interactive session 
   ...
   >>>
   

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Python interpreter and Interactive Development Environments (IDEs) 

  Python interpreter
    Can only import module into python interpreter ONCE (Why?) (demo)

  IDLE
   IDE included with Python from python.org
   Interpreter - much like command-line Python
   Editor - Python-aware - knows about indentation, keywords
   Can reload revised module into interpreter without exit, restart 
   
  In IDLE editor, F5 (run this module) is like python -i module.py
   but without restarting IDLE  
   
  Others
   IPython - popular for scientific computing, includes graphics a la MATLAB,
    can reload modules without losing context (variables, etc.)
   BPython, ... many others ...