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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Catching the fishes first?

If you make a fish pie for your friends, you'll catch all the fish you need before you start the preparation and cooking work, and you'll do the cooking all at once.

If you run a fish pie factory, you'll have a steady flow of fish arriving while your production line is running. Receiving all the fish you need before you start production each week would give you a major storage problem (inside) or an issue with some rathe keen gulls (outside).

In Python, you can iterate through a list - and that's fine for the smaller cases. But in cases where you have a substantial amount of data, you should read / request / work it out on a "just in time" basis, using a generator function.

Here's an example piece of code to show you how ...

  # Getting all the fish at once
  
  def getvals(top):
  stuff = []
    vat = 0
    while vat < top:
      print "caught mackrel no",vat
      stuff.append(vat)
      vat += 1
    return stuff
  
  # Just in time
  
  def xgetvals(top):
    vat = 0
    while vat < top:
      print "caught mackrel no",vat
      yield vat
      vat += 1
  
  ending = 15
  
  for value in getvals(ending):
    print "Added to pie",value
  
  for value in xgetvals(ending):
    print "Added to pie",value


(written 2011-09-27, updated 2011-09-28)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y105 - Python - Functions, Modules and Packages
  [96] Variable Scope - (2004-10-22)
  [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)
  [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)


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Away to train - but still around by video for Melksham meetings
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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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