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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Variable Scope

One of the vital topics on all our programming courses is that of variable scope. Variable Scope may be defined as the area of a program in which a variable is visible, and how long that variable is accessible for.

Why do I describe variable scope as a vital subject when you can write simple programs in almost any of the languages we teach without any appreciation of the issue? Because it becomes vital as your code grows into a series of blocks - sometimes named (functions in PHP, procs in Tcl, def in Python, subs in Perl, methods in Java) and sometimes not (for example { to } blocks in Perl, inset blocks in Python). As a new programmer, you might think that all variables should be visible everywhere (this is often know as "default global"), but that's a bad default - the only language that has this default is Perl and that's for historic reasons. It will change at Perl 6!

Why is "default global" a bad default? Because it means that when you combine code from two blocks / files / sources, each must have variables who's names don't conflict with and other name in any other module and in practice that's almost impossible to ensure. Looking at a real-life example, in our household "Charlie" refers to the cat, but in the Royal Family "Charlie" might be used to refer to the Prince of Wales. Let's say that the Royal family comes to visit us (yeah, improbable I know!), and someone says "come here Charlie" .... are they going to get a cat or a prince?
(written 2004-10-22, updated 2008-05-11)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Z203 - Cat and Dog
  [62] Technical Open House - (2004-09-25)
  [547] Taking the dog for a walk - (2005-12-29)
  [744] We can offer a room, but we can't operate on a dog - (2006-06-05)
  [771] From cat breeder to Cobol to Perl - (2006-06-21)
  [2029] Also for the eyes of the cat - (2009-02-07)
  [2132] Learning about Lurchers - (2009-04-18)
  [2138] Ski bore ... train bore ... dog bore - (2009-04-24)
  [2140] Beware - giving copyright away when you upload a picture - Dogs Trust - (2009-04-25)
  [2167] Watching the tele - (2009-05-10)
  [2252] Leaping dog, Leaping horse, copyright of old masters - (2009-06-20)
  [2271] Dogs Trust, Dog Show, Newbury - (2009-07-06)
  [2295] The dog is not in trouble - (2009-07-17)
  [2450] Family Gathering at 404, The Spa - (2009-10-11)
  [2451] Gypsy says - (2009-10-12)
  [2456] Bright Eyes - (2009-10-16)
  [2496] A better design of mouth - (2009-11-07)
  [2499] ourdog is Greyhound, Staffie and Ginger Cake - (2009-11-09)
  [2555] Bookkeeping - (2009-12-29)
  [2689] Can my dog eat potatoes? Doggie Dietary Research, and political sleaze! - (2010-03-23)
  [2787] Sleeping in on Sunday - (2010-05-30)
  [2897] The Land of the Black Labrador - (2010-08-01)
  [3096] Contrast in pictures - (2010-12-20)
  [3324] Rabbit Shelter - (2011-06-12)
  [3338] Return trip - Dogs Trust, Newbury - (2011-06-27)
  [3530] A typical weekend?? - (2011-11-28)
  [3533] No message - just doggy pictures of the new doggy - (2011-11-30)
  [3537] Letting the foster parents know ... too little or too much? - (2011-12-04)
  [3541] I loves Melksham - (2011-12-06)
  [3553] Changes to morning routines - (2011-12-16)
  [3561] Happy Christmas ... a Christmas morning walk in Melksham - (2011-12-25)
  [3606] Gypsy and Billy enjoy the snow - (2012-02-10)
  [3625] An update on Billy the Greyhound and Gypsy the Lurcher - (2012-02-25)
  [3674] Off to walk the dogs - (2012-03-30)
  [3675] Spring 2012 - (2012-03-30)
  [3737] Postcards from Barmouth - (2012-05-20)
  [3906] Taking the lead, not the dog, for a walk. - (2012-10-28)
  [3908] Black dogs at Halloween - (2012-10-31)
  [3920] Challenge for a photographer - (2012-11-10)
  [3936] Lisa is home today ... - (2012-11-26)
  [3943] With us for a year already! - (2012-12-03)
  [4016] Red, yellow, green or pink dog? Yellow Dog Project - (2013-02-23)
  [4130] Soft furnishings up a Welsh Mountain - (2013-07-03)
  [4180] Exceptionally, I sign a petition - on a life and death issue for Irish dogs - (2013-09-20)
  [4189] Who are we - Lisa, Graham, Gypsy and Billy - (2013-10-07)
  [4316] Too many Staffies, too many lurchers - (2014-11-16)
  [4333] Misty Melksham Morning - (2014-11-30)
  [4417] Crisp morning, fast run - (2015-02-06)
  [4433] Different views of a Welsh Valley - but headed home - (2015-02-20)
  [4507] In favour of adoption rather than puppy purchase - dogs! - (2015-06-07)
  [4517] Black dog day - and Bobby still seeks his new home - (2015-09-26)
  [4526] Day trip to Lancaster - (2015-10-10)
  [4666] Spring at Well House Manor - (2016-03-27)

Y105 - Python - Functions, Modules and Packages
  [105] Distance Learning - (2004-10-31)
  [294] Python generator functions, lambdas, and iterators - (2005-04-28)
  [303] Lambdas in Python - (2005-05-06)
  [308] Call by name v call by value - (2005-05-11)
  [340] Code and code maintainance efficiency - (2005-06-08)
  [386] What is a callback? - (2005-07-22)
  [418] Difference between import and from in Python - (2005-08-18)
  [561] Python's Generator functions - (2006-01-11)
  [668] Python - block insets help with documentation - (2006-04-04)
  [745] Python modules. The distribution, The Cheese Shop and the Vaults of Parnassus. - (2006-06-05)
  [749] Cottage industry or production line data handling methods - (2006-06-07)
  [775] Do not duplicate your code - (2006-06-23)
  [821] Dynamic functions and names - Python - (2006-08-03)
  [900] Python - function v method - (2006-10-20)
  [912] Recursion in Python - (2006-11-02)
  [913] Python - A list of methods - (2006-11-03)
  [949] Sludge off the mountain, and Python and PHP - (2006-11-27)
  [959] It's the 1st, not the 1nd 1rd or 1th. - (2006-12-01)
  [1134] Function / method parameters with * and ** in Python - (2007-04-04)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)
  [1202] Returning multiple values from a function (Perl, PHP, Python) - (2007-05-24)
  [1464] Python Script - easy examples of lots of basics - (2007-12-08)
  [1784] Global - Tcl, PHP, Python - (2008-09-03)
  [1790] Sharing variables with functions, but keeping them local too - Python - (2008-09-09)
  [1869] Anonymous functions (lambdas) and map in Python - (2008-11-04)
  [1870] What to do with a huge crop of apples - (2008-11-04)
  [1871] Optional and named parameters in Python - (2008-11-05)
  [1879] Dynamic code - Python - (2008-11-11)
  [2011] Conversion of OSI grid references to Eastings and Northings - (2009-01-28)
  [2439] Multiple returns from a function in Python - (2009-10-06)
  [2440] Optional parameters to Python functions - (2009-10-07)
  [2481] Sample code with errors in it on our web site - (2009-10-29)
  [2506] Good example of recursion in Python - analyse an RSS feed - (2009-11-18)
  [2520] Global and Enable - two misused words! - (2009-11-30)
  [2718] Python - access to variables in the outer scope - (2010-04-12)
  [2766] Optional and named parameters to Python functions/methods - (2010-05-15)
  [2878] Program for reliability and efficiency - do not duplicate, but rather share and re-use - (2010-07-19)
  [2929] Passing a variable number of parameters in to a function / method - (2010-08-20)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [2998] Using an exception to initialise a static variable in a Python function / method - (2010-10-13)
  [3159] Returning multiple values from a function call in various languages - a comparison - (2011-02-06)
  [3280] Passing parameters to Python functions - the options you have - (2011-05-07)
  [3459] Catching the fishes first? - (2011-09-27)
  [3464] Passing optional and named parameters to python methods - (2011-10-04)
  [3472] Static variables in functions - and better ways using objects - (2011-10-10)
  [3474] Python Packages - groupings of modules. An introduction - (2011-10-11)
  [3662] Finding all the unique lines in a file, using Python or Perl - (2012-03-20)
  [3695] Functions are first class variables in Lua and Python - (2012-04-13)
  [3766] Python timing - when to use a list, and when to use a generator - (2012-06-16)
  [3852] Static variables in Python? - (2012-08-29)
  [3885] Default local - a good choice by the author of Python - (2012-10-08)
  [3931] Optional positional and named parameters in Python - (2012-11-23)
  [3945] vargs in Python - how to call a method with unknown number of parameters - (2012-12-06)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04)
  [4161] Python varables - checking existance, and call by name or by value? - (2013-08-27)
  [4212] Python functions - an introduction to how they work - (2013-11-16)
  [4361] Multiple yields and no loops in a Python generator? - (2014-12-22)
  [4407] Python - even named code blocks are objects - (2015-01-28)
  [4410] A good example of recursion - a real use in Python - (2015-02-01)
  [4441] Reading command line parameters in Python - (2015-02-23)
  [4448] What is the difference between a function and a method? - (2015-03-04)
  [4645] What are callbacks? Why use them? An example in Python - (2016-02-11)
  [4662] Recursion in Python - the classic example - (2016-03-07)
  [4719] Nesting decorators - (2016-11-02)
  [4722] Embedding more complex code into a named block - (2016-11-04)
  [4724] From and Import in Python - where is the module loaded from? - (2016-11-06)

T207 - Tcl/Tk - Procedures and Variable Scope
  [122] Passing arrays to procs in Tcl - (2004-11-18)
  [409] Functions and commands with dangerous names - (2005-08-11)
  [1404] Tcl - global, upvar and uplevel. - (2007-10-24)
  [1782] Calling procs in Tcl and how it compares to Perl - (2008-09-02)
  [2466] Tcl - passing arrays and strings in and back out of procs - (2009-10-22)
  [2476] Tcl - uplevel to run code at calling level - (2009-10-24)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [3414] Passing back multiple results in Tcl - upvar and uplevel - (2011-09-01)
  [3629] Sharing lots of values in Tcl without having lots of global declarations - (2012-02-28)
  [4398] Accessing variables across subroutine boundaries - Perl, Python, Java and Tcl - (2015-01-18)

P209 - Subroutines in Perl
  [357] Where do Perl modules load from - (2005-06-24)
  [531] Packages in packages in Perl - (2005-12-16)
  [588] Changing @INC - where Perl loads its modules - (2006-02-02)
  [969] Perl - $_ and @_ - (2006-12-07)
  [1826] Perl - Subs, Chop v Chomp, => v , - (2008-10-08)
  [1850] Daisy the Cow and a Pint of Ginger Beer - (2008-10-21)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [1921] Romeo and Julie - (2008-12-04)
  [2069] Efficient calls to subs in Perl - avoid duplication, gain speed - (2009-03-07)
  [2550] Do not copy and paste code - there are much better ways - (2009-12-26)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [3066] Separating groups of variables into namespaces - (2010-11-24)
  [3574] Perl functions such as chop change their input parameters - (2012-01-10)
  [3833] Learning to use existing classes in Perl - (2012-08-10)

J706 - Java - Objects and Classes
  [477] Class, static and unbound variables - (2005-10-25)
  [1296] An example of Java Inheritance from scratch - (2007-08-08)
  [1500] First Class Java. First step and moving forward. - (2008-01-10)
  [1906] Long, Longer, Longest in Java - (2008-11-25)
  [1925] Introduction to Object Oriented Programming - (2008-12-06)
  [2169] When should I use OO techniques? - (2009-05-11)
  [2422] Looking inside Java classes - javap and javadoc - (2009-09-25)
  [2616] Defining a static method - Java, Python and Ruby - (2010-02-01)
  [2651] Calculation within objects - early, last minute, or cached? - (2010-02-26)
  [4413] Binomial Coefficient (Pascal Triangle) objects in Java - (2015-02-03)
  [4422] Objects - from physical to virtual or abstract - Java - (2015-02-10)

H105 - PHP - Functions
  [223] There is a function in PHP to do that - (2005-02-21)
  [339] Passing information into and out of PHP functions - (2005-06-07)
  [421] Don't repeat code - use loops or functions - (2005-08-21)
  [866] A lazy programmer is a good programmer - (2006-09-15)
  [936] Global, Superglobal, Session variables - scope and persistance in PHP - (2006-11-21)
  [1021] PHP - static declaration - (2007-01-04)
  [1267] is there a lookup function in php? - (2007-07-15)
  [1357] Clean my plate, but keep my wine bottle. (PHP; Static) - (2007-09-18)
  [1380] Static variables in PHP - (2007-10-05)
  [2488] A variable number of arguments in a PHP function - (2009-11-02)
  [2630] Static variables and ampersands in PHP - (2010-02-10)
  [2682] Adding extensions to PHP Open Source applications - callbacks - (2010-03-17)
  [2737] Improving your function calls (APIs) - General and PHP - (2010-04-24)
  [3026] Coding efficiency - do not repeat yourself! - (2010-11-02)


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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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