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Practical polymorphism in action

Polymorphism is the ability of a piece of common code to process a piece of data in different ways depending on its type. It's a great facility, talked about a lot in theory and on courses ... but then what about its practical use? Here's a very simple little example from last week, showing how a file, another process on the computer you're using, and even a remote web page can be read in as data through the same (polymorphic) code with python's readlines method(s).

# Three ALTERNATIVE opens - just use the one you need
# from another process
from os import *
fh = popen("df -k")

# from a remote URL
import urllib
fh = urllib.urlopen("http://www.sheepbingo.co.uk")

# from a local file ...
fh = open("localfile.txt")

# ... whichever way you open your STREAM, you can readlines it!
for info in fh.readlines():
  print info,

(written 2006-12-04)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y112 - Python - Objects - Intermediate
  [4719] Nesting decorators - (2016-11-02)
  [4718] Defining an object that is a modified standard type in Python - (2016-11-02)
  [4717] with in Python - examples of use, and of defining your own context - (2016-11-02)
  [4649] Object and Static methods - what is the difference; example in Python 3 - (2016-02-17)
  [4541] Setting up and tearing down with the Python with keyword - (2015-10-16)
  [4450] Deciding whether to use parameters, conditional statements or subclasses - (2015-03-05)
  [4449] Spike solution, refactoring into encapsulated object methods - good design practise - (2015-03-05)
  [4410] A good example of recursion - a real use in Python - (2015-02-01)
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [4356] Object factories in C++, Python, PHP and Perl - (2014-12-19)
  [4344] Python base and inherited classes, test harness and unit testing - new examples - (2014-12-07)
  [4094] Python Properties - how and why - (2013-05-18)
  [4028] Really Simple Class and Inheritance example in Python - (2013-03-04)
  [3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
  [3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
  [3524] Metaclasses (Python) and Metatables (Lua) - (2011-11-17)
  [3472] Static variables in functions - and better ways using objects - (2011-10-10)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [3002] A list of special method and attribute names in Python - (2010-10-17)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [2905] Defining static methods in Python - (2010-08-05)
  [2889] Should Python classes each be in their own file? - (2010-07-27)
  [2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
  [2764] Python decorators - your own, staticmethod and classmethod - (2010-05-14)
  [2722] Mixins example in Python - (2010-04-14)
  [2720] Multiple inheritance in Python - complete working example - (2010-04-14)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2693] Methods that run on classes (static methods) in Python - (2010-03-25)
  [2485] How do I set up a constant in Python? - (2009-10-31)
  [2409] TypeError: super() argument 1 must be type, not classobj (Python) - (2009-09-18)
  [2368] Python - fresh examples of all the fundamentals - (2009-08-20)
  [1819] Calling base class constructors - (2008-10-03)
  [1661] Equality, sameness and identity - Python - (2008-05-31)
  [1644] Using a utility method to construct objects of different types - Python - (2008-05-17)
  [1517] Python - formatting objects - (2008-01-24)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [1146] __new__ v __init__ - python constructor alternatives? - (2007-04-14)
  [903] Pieces of Python - (2006-10-23)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [477] Class, static and unbound variables - (2005-10-25)
  [383] Overloading of operators on standard objects in Python - (2005-07-19)
  [296] Using a Python dictionary as a holder of object attributes - (2005-04-30)

Y301 - Python - Class Interaction - an example
  [236] Tapping in on resources - (2005-03-05)


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