Training, Open Source Programming Languages

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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.
Passing optional and named parameters to python methods

When you call a named block of code (a method or function), you'll wish to pass in originating values that are changed from one call / use to the next - these are commonly known as the parameters. If I'm calling a function to calculate the area of a rectangle, for example, I would pass in the width and height, and if I'm calling a function to input a number from the keyboard I'm probably going to pass in the prompt message, and a minimum and maximum acceptable value.

There are some time, though, when you may want to leave out a parameter - let it be assumed. If I want to connect to a database, "localhost" would be a fair assumption if a host name is not given, for example.

In Python, I can specify optional parameters within the function definition by giving a name and assigning them to a default value, for example:
  def getload(lenny, seats, factor = 1.4):
will define a function that takes 2 or 3 parameters; if only 2 are specified, then the third one will take the assumed value of 1.4.

There are also times where you may wish to call your function with an indeterminate (and varying) number of parameters, and in this case you can add a * in front of the final named parameter and it will act as a sponge, gathering all remaining positional parameters into a list, for example:
  def average(first, *rest):
which is a function with at least one (but as many as you like) parameters. In practise, this isn't used all that often as it's far better to pass in a single list object from the calling code than to build a list of individual objects within the function in most circumstances.

Another possibility is that you may wish to call a function that could take a very large number of potentially different parameters, and they could be specified in any order. In Python, you can use named parameters by adding ** in front of the final parameter and you'll then be able to collect a dictionary of values. The function definition may look like:
  def bob(fred, cat="fullofbird", *rabbits, **kx):
with named parameters being collected in a dictionary called kx. Here's a sample call:
  bob(44,55,66,teeth=45,legs=3, arms=4)

Sample functions, and calls, shown above are in sample programs on our web site [here] and [here].




If you want to define the ultimate, generic function that will accept anything thrown at it, you can write your definition using the following structure:
  def wrapped(*args, **kwargs)

And if you want to call a function passing in such generics, you can do so in a similar way:
  finalanswer = why(*args, **kwargs)

Both of these example lines are taken from a recent example ([here]) I wrote to demonstrate decorators - wrappers that you can apply to functions or methods in Python for purposes such as logging calls and producing code coverage maps.
(written 2011-10-04)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y212 - Python - Code testing, patterns, profiles and optimisation.
  [235] Preparation for a day's work - (2005-03-04)
  [1140] Python GTK - Widget, Packing, Event and Feedback example - (2007-04-09)
  [1146] __new__ v __init__ - python constructor alternatives? - (2007-04-14)
  [1148] Python decorators - wrapping a method call in extra code - (2007-04-15)
  [1555] Advanced Python, Perl, PHP and Tcl training courses / classes - (2008-02-25)
  [2123] Using Python with OpenOffice - (2009-04-09)
  [2616] Defining a static method - Java, Python and Ruby - (2010-02-01)
  [3441] Pressing ^C in a Python program. Also Progress Bar. - (2011-09-15)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [3478] Testing your Python classes with the unittest package - how to - (2011-10-14)
  [3658] Using Make for a distribution - (2012-03-17)
  [4090] Test Driven Development in Python - Customer Comes First - (2013-05-16)
  [4326] Learning to program - comments, documentation and test code - (2014-11-22)
  [4344] Python base and inherited classes, test harness and unit testing - new examples - (2014-12-07)
  [4446] Combining tests into suites, and suites into bigger suites - Python and unittest - (2015-03-01)
  [4470] Testing in Python 3 - unittest, doctest and __name__ == __main__ too. - (2015-04-21)
  [4538] Flask and unittest - hello web app test world - (2015-10-15)
  [4540] Unittest of a Flask application including forms - (2015-10-15)
  [4542] The principle of mocking - and the Python Mock package - (2015-10-17)
  [4617] Pytest - starting example - (2016-01-07)
  [4618] Pytest - second example beyond hello world - (2016-01-08)
  [4716] Profiling your Python program - (2016-11-01)

Y107 - Python - Dictionaries
  [103] Can't resist writing about Python - (2004-10-29)
  [955] Python collections - mutable and imutable - (2006-11-29)
  [1144] Python dictionary for quick look ups - (2007-04-12)
  [1145] Using a list of keys and a list of values to make a dictionary in Python - zip - (2007-04-13)
  [2368] Python - fresh examples of all the fundamentals - (2009-08-20)
  [2915] Looking up a value by key - associative arrays / Hashes / Dictionaries - (2010-08-11)
  [2986] Python dictionaries - reaching to new uses - (2010-10-05)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [3488] Python sets and frozensets - what are they? - (2011-10-20)
  [3554] Learning more about our web site - and learning how to learn about yours - (2011-12-17)
  [3555] Football league tables - under old and new point system. Python program. - (2011-12-18)
  [3662] Finding all the unique lines in a file, using Python or Perl - (2012-03-20)
  [3934] Multiple identical keys in a Python dict - yes, you can! - (2012-11-24)
  [4027] Collections in Python - list tuple dict and string. - (2013-03-04)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04)
  [4409] Setting up and using a dict in Python - simple first example - (2015-01-30)
  [4469] Sorting in Python 3 - and how it differs from Python 2 sorting - (2015-04-20)
  [4661] Unique word locator - Python dict example - (2016-03-06)
  [4668] Sorting a dict in Python - (2016-04-01)

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)
  [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)
  [3472] Static variables in functions - and better ways using objects - (2011-10-10)
  [3474] Python Packages - groupings of modules. An introduction - (2011-10-11)
  [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)
  [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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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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