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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.
Take the dog on a lead - do not carry her. Perl references.

Taking the dog out for a walk? It's much easier to use a lead than to carry the whole dog.

And ... in a similar vein ... when you're passing some data into a named block of code (a.k.a. sub, subroutine, function, procedure, command, method, macro) when programming, it's much more efficient to pass in a pointeri (a.k.a. an address or a reference)

When you pass in a pointer, you're saving yourself having to duplicate the data. That can be a serious saving if you're working with large or huge data sets. And you're also providing a powerful (but dangerous if misused) capability of altering the original data within the code that you've called.

On yesterday's Perl course, I wrote a fresh example that compares copying a list into a Perl sub, and passing in the address. The difference is just a \ !


Copying into the sub:
  addon("Ibiza",@places);

Passing a reference into the sub:
  anotheradd("Magaluf",\@places);

Full source code of the demo [here], including the source of the subs which must (of course) be coded to accept the data type that's being passed to them.




Perl's references are also an excellent way of setting up collections of collections - a very flexible and space-saving alternative to the multidimensional arrays of other languages. New example of those - [here].
(written 2011-09-17, updated 2013-01-01)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P217 - Perl - More than Simple Lists and Hashes!
  [43] Hash of lists in Perl - (2004-09-09)
  [293] Course follow-ups - (2005-04-27)
  [1514] Autovivification - the magic appearance of variables in Perl - (2008-01-21)
  [2241] Perl references - $$var and \$var notations - (2009-06-15)
  [2840] Just pass a pointer - do not duplicate the data - (2010-06-30)
  [2877] Further more advanced Perl examples - (2010-07-19)
  [2996] Copying - duplicating data, or just adding a name? Perl and Python compared - (2010-10-12)
  [3007] Setting up a matrix of data (2D array) for processing in your program - (2010-10-21)
  [3072] Finding elements common to many lists / arrays - (2010-11-26)
  [3105] Adventure with references to lists and lists of references - (2010-12-26)
  [3118] Arrays of arrays - or 2D arrays. How to program tables. - (2011-01-02)
  [3399] From fish, loaves and apples to money, plastic cards and BACS (Perl references explained) - (2011-08-20)
  [3406] Not multidimentional arrays - but lists of lists. Much more flexible. Perl! - (2011-08-26)
  [3577] How to do multidimensional arrays (or rather lists and hashes) in Perl - (2012-01-14)
  [3906] Taking the lead, not the dog, for a walk. - (2012-10-28)


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Perl and CGI - simple form, and monitoring script.
Some other Articles
Checking all the systems on a subnet, using Expect and Tk
Needle in a haystack - finding the web server overload
Awk v Perl
Perl and CGI - simple form, and monitoring script.
Take the dog on a lead - do not carry her. Perl references.
Getting more log information from the Apache http web server
A demonstration of how many Python facilities work together
Pressing ^C in a Python program. Also Progress Bar.
Research is exciting. But should routine be automated?
Python for loops - applying a temporary second name to the same object
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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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