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Program for reliability and efficiency - do not duplicate, but rather share and re-use

Being trained in PythonWhen you're writing a new piece of code - especially if you're also quite new to programming - you'll be concentrating so much on getting it to work that you may not be giving too much thought to making it easy look after your code later on (maintainance), nor to sharing a piece of code between programs. But in the medium and longterm, if you can avoid duplicating code you'll be saving yourself and you colleagues a lot of time and effort!

• If you find yourself copying and pasting a block of code, there's probably an easier way!

• If you duplicate a block of code, but then alter a few elements, don't say "that's not a duplicate" - say "I have identified which values will be parameters to a function"

I have an example here from a Python course at the start of last week. Look at this code:


while True:
        him = int(raw_input("How many years old is he? "))
        if him < 0 or him > 119:
                continue
        break
 
while True:
        her = int(raw_input("How many years old is she? "))
        if her < 0 or her > 119:
                continue
        break


Delegate, LymingtonIt's almost exactly the same block of code - just the prompt and the result variable are changed, and a good case to make a named block of code. This is Python, so we used "def" but it could have been sub in Perl, function in PHP, or proc in Tcl.

The function code has to be defined before it is called - here's my example:


def getage(person_word):
    while True:
        question = "How many years old is " + person_word + "? "
        age = int(raw_input(question))
        if age < 0 or age > 119:
            continue
        break
    return age


That does not run the code - it just defines it. You then call it by name, passing in the string that contains the person_word, and returning the result to another variable:

him = getage("he")
her = getage("she")


Python course delegateTaking that a step further, you'll want to share the code between programs. You can do that by putting your defined function into a shared file (usually alongside other functions that are to be shared) which you will then pull in as required in some way. In Perl, that would be a use or a require, in Tcl it would be a source, and in Python it would be a from or an import.

Structure your code well using these techniques - not only will you find you're making huge time savings in the long term, but you'll find that you're also wring more consistent and reliable programs - and that the benefits come in the short term too. Did I tell you that by naming a block of code, you provide a unit of code that's much easier to test and debug ... with a built in test routine and documentation too!


Full source code links:

Control case with repeated code
Re-use within the same source file
Separated out for sharing with other programs and the shared file

Illustrations - delegates on last week's Python Course
(written 2010-07-19, updated 2010-07-30)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Q101 - Object Orientation and General technical topics - Programming Principles
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  [4632] Remember to ask the question before you listen for the answer - (2016-01-26)
  [4611] Hungarian, Camel, Snake and Kebab - variable naming conventions - (2016-01-03)
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  [4118] We not only teach PHP and Python - we teach good PHP and Python Practice! - (2013-06-18)
  [4090] Test Driven Development in Python - Customer Comes First - (2013-05-16)
  [4061] Seamless, integrated IT - we have a long way to go! - (2013-04-11)
  [4003] Web and console - same principle, same code - Ruby example - (2013-02-14)
  [3954] Lesson 1 in programing - write clean, reuseable and maintainable tidy code - (2012-12-16)
  [3928] Storing your intermediate data - what format should you you choose? - (2012-11-20)
  [3878] From Structured to Object Oriented Programming. - (2012-10-02)
  [3673] Object oriented or structured - a comparison in Python. Also writing clean regular expressions - (2012-03-26)
  [3551] Some terms used in programming (Biased towards Python) - (2011-12-12)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3542] What order are operations performed in, in a Perl expression? - (2011-12-07)
  [3456] Stepping stones - early coding, and writing re-usable code quickly - (2011-09-24)
  [3026] Coding efficiency - do not repeat yourself! - (2010-11-02)
  [2964] An introduction to file handling in programs - buffering, standard in and out, and file handles - (2010-09-21)
  [2915] Looking up a value by key - associative arrays / Hashes / Dictionaries - (2010-08-11)
  [2769] Easy - but for whom? - (2010-05-18)
  [2737] Improving your function calls (APIs) - General and PHP - (2010-04-24)
  [2586] And and Or illustrated by locks - (2010-01-17)
  [2550] Do not copy and paste code - there are much better ways - (2009-12-26)
  [2510] The music of the stock market - (2009-11-22)
  [2415] Variable names like i and j - why? - (2009-09-22)
  [2327] Planning! - (2009-08-08)
  [2310] Learning to write high quality code in Lua - (2009-07-30)
  [2228] Where do I start when writing a program? - (2009-06-11)
  [2022] Pre and post increment - the ++ operator - (2009-02-03)
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Q907 - Object Orientation and General technical topics - Object Orientation: Design Techniques
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  [4449] Spike solution, refactoring into encapsulated object methods - good design practise - (2015-03-05)
  [4430] The spirit of Java - delegating to classes - (2015-02-18)
  [4374] Test driven development, and class design, from first principles (using C++) - (2014-12-30)
  [4098] Using object orientation for non-physical objects - (2013-05-22)
  [3978] Teaching OO - how to avoid lots of window switching early on - (2013-01-17)
  [3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
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  [3798] When you should use Object Orientation even in a short program - Python example - (2012-07-06)
  [3763] Spike solutions and refactoring - a Python example - (2012-06-13)
  [3760] Why you should use objects even for short data manipulation programs in Ruby - (2012-06-10)
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  [3454] Your PHP website - how to factor and refactor to reduce growing pains - (2011-09-24)
  [3260] Ruby - a training example that puts many language elements together to demonstrate the whole - (2011-04-23)
  [3085] Object Oriented Programming for Structured Programmers - conversion training - (2010-12-14)
  [3063] Comments in and on Perl - a case for extreme OO programming - (2010-11-21)
  [2977] What is a factory method and why use one? - Example in Ruby - (2010-09-30)
  [2953] Turning an exercise into the real thing with extreme programming - (2010-09-11)
  [2889] Should Python classes each be in their own file? - (2010-07-27)
  [2865] Relationships between Java classes - inheritance, packaging and others - (2010-07-10)
  [2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
  [2747] Containment, Associative Objects, Inheritance, packages and modules - (2010-04-30)
  [2741] What is a factory? - (2010-04-26)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
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  [507] Introduction to Object Oriented Programming - (2005-11-27)
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Y105 - Python - Functions, Modules and Packages
  [4724] From and Import in Python - where is the module loaded from? - (2016-11-06)
  [4722] Embedding more complex code into a named block - (2016-11-04)
  [4719] Nesting decorators - (2016-11-02)
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  [1879] Dynamic code - Python - (2008-11-11)
  [1871] Optional and named parameters in Python - (2008-11-05)
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  [1869] Anonymous functions (lambdas) and map in Python - (2008-11-04)
  [1790] Sharing variables with functions, but keeping them local too - Python - (2008-09-09)
  [1784] Global - Tcl, PHP, Python - (2008-09-03)
  [1464] Python Script - easy examples of lots of basics - (2007-12-08)
  [1202] Returning multiple values from a function (Perl, PHP, Python) - (2007-05-24)
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  [1134] Function / method parameters with * and ** in Python - (2007-04-04)
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  [900] Python - function v method - (2006-10-20)
  [821] Dynamic functions and names - Python - (2006-08-03)
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  [561] Python's Generator functions - (2006-01-11)
  [418] Difference between import and from in Python - (2005-08-18)
  [386] What is a callback? - (2005-07-22)
  [340] Code and code maintainance efficiency - (2005-06-08)
  [308] Call by name v call by value - (2005-05-11)
  [303] Lambdas in Python - (2005-05-06)
  [294] Python generator functions, lambdas, and iterators - (2005-04-28)
  [105] Distance Learning - (2004-10-31)
  [96] Variable Scope - (2004-10-22)


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Night Porter and reception - 24 hours a day?
Program for reliability and efficiency - do not duplicate, but rather share and re-use
Further more advanced Perl examples
Different perl examples - some corners I rarely explore
A long day in Melksham ...
Unpacking a Perl string into a list
Another toot of the trumpet
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