"A Metaclass (Python) or Metatable (Lua) adds extra code / data / behaviour to an object, table, or class."
What does that mean? It means that I can define a behavior that I want to be shared, that I want to define at run-time, that I want to amend ... in a separate module / zone / table from my main class. It's flexible, powerful. In Lua, it's a vital feature if you're looking to write code using an Object Oriented paradigm, as your metatable provides you with your methods which are able to be shared between objects. In Python, it's rather esoteric - yes, useful but you'll tend to write code which all but the most hardened of programmers will end up scratching their heads over.
Anyway - new Python examples
[here]. Lua example
[here], and a further description with examples
[here]. That latter example makes good reading on the principles for Python users as well as Lua users.
Our
Lua Courses all cover Metatables. Our
Python Courses do not at present cover metaclasses; your instructor will be happy to answer questions on them, demonstrate them if you ask, cover them on extra days or after class. He will raise them if they look to be useful based on your description of your applications .. but for the most part they're something that few Python application programmers will be using, however internally important they are -
and it's part of a trainer's job to pick out the important things for YOU! (written 2011-11-17, updated 2011-12-03)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y112 - Python - Objects - Intermediate [296] Using a Python dictionary as a holder of object attributes - (2005-04-30)
[383] Overloading of operators on standard objects in Python - (2005-07-19)
[477] Class, static and unbound variables - (2005-10-25)
[656] Think about your design even if you don't use full UML - (2006-03-24)
[831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
[903] Pieces of Python - (2006-10-23)
[964] Practical polymorphism in action - (2006-12-04)
[1146] __new__ v __init__ - python constructor alternatives? - (2007-04-14)
[1217] What are factory and singleton classes? - (2007-06-04)
[1517] Python - formatting objects - (2008-01-24)
[1644] Using a utility method to construct objects of different types - Python - (2008-05-17)
[1661] Equality, sameness and identity - Python - (2008-05-31)
[1819] Calling base class constructors - (2008-10-03)
[2368] Python - fresh examples of all the fundamentals - (2009-08-20)
[2409] TypeError: super() argument 1 must be type, not classobj (Python) - (2009-09-18)
[2485] How do I set up a constant in Python? - (2009-10-31)
[2693] Methods that run on classes (static methods) in Python - (2010-03-25)
[2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
[2720] Multiple inheritance in Python - complete working example - (2010-04-14)
[2722] Mixins example in Python - (2010-04-14)
[2764] Python decorators - your own, staticmethod and classmethod - (2010-05-14)
[2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
[2889] Should Python classes each be in their own file? - (2010-07-27)
[2905] Defining static methods in Python - (2010-08-05)
[2994] Python - some common questions answered in code examples - (2010-10-10)
[3002] A list of special method and attribute names in Python - (2010-10-17)
[3442] A demonstration of how many Python facilities work together - (2011-09-16)
[3472] Static variables in functions - and better ways using objects - (2011-10-10)
[3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
[3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
[4028] Really Simple Class and Inheritance example in Python - (2013-03-04)
[4094] Python Properties - how and why - (2013-05-18)
[4344] Python base and inherited classes, test harness and unit testing - new examples - (2014-12-07)
[4356] Object factories in C++, Python, PHP and Perl - (2014-12-19)
[4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
[4410] A good example of recursion - a real use in Python - (2015-02-01)
[4449] Spike solution, refactoring into encapsulated object methods - good design practise - (2015-03-05)
[4450] Deciding whether to use parameters, conditional statements or subclasses - (2015-03-05)
[4541] Setting up and tearing down with the Python with keyword - (2015-10-16)
[4649] Object and Static methods - what is the difference; example in Python 3 - (2016-02-17)
[4717] with in Python - examples of use, and of defining your own context - (2016-11-02)
[4718] Defining an object that is a modified standard type in Python - (2016-11-02)
[4719] Nesting decorators - (2016-11-02)
U107 - Object Orientation - the Lua way [1692] Towards Object Oriented Programming in Lua - (2008-06-30)
[1699] If you are learning Lua, here are some more examples - (2008-07-06)
[1743] First class functions in Lua lead to powerful OO facilities - (2008-08-07)
[2318] For Lua Programmers AND for Town Planners - (2009-08-02)
[2359] A fresh example - objects the Lua way - (2009-08-13)
[2455] Lua examples - coroutines, error handling, objects, etc - (2009-10-15)
[2701] Is Lua an Object Oriented language? - (2010-04-01)
[2703] Lua Metatables - (2010-04-02)
[2710] __index and __newindex in Lua - metatable methods - (2010-04-05)
[3142] Private and Public - and things between - (2011-01-22)
[3396] Tables as Objects in Lua - a gentle introduction to data driven programming - (2011-08-17)
[3683] Weak references in Lua - what are they, and why use them? - (2012-04-04)
[3694] Special __ methods you can use in Lua metatables - (2012-04-12)
[3727] Using Lua tables as objects - (2012-05-11)
[3730] What is a metatable? How do I set one up? How do I use them? Lua - (2012-05-12)
[4117] Is Lua an Object Oriented language? - (2013-06-15)
[4248] Metatables, Metamethods, classes and objects in Lua - (2014-03-18)
[4273] Dot or Colon separator between table name and member in Lua - what is the difference? - (2014-05-06)
[4572] Tables with values and code in Lua - looks like an object? - (2015-11-05)
[4573] Classic style OO code - in Lua - (2015-11-05)
[4753] Lua, Tcl, Python, C and C++ courses - at our Melksham HQ or on your site - forward from July 2017 - (2017-07-02)
Some other Articles
December courses - PHP, Python, Perl - and a weekend Lua courseMelksham - changing times, an opportunity for the futureMelksham has a Heart - Montage picture for saleMelksham has a heart - come and see the pictures. Sunday, 11 to 3, Assembly HallMetaclasses (Python) and Metatables (Lua)When competition is not a good idea - Melksham Bus AbsurdityNetworking - North and West Wilts FSB StyleEmergency First Aid at Work (HSE) training in Melksham - places available for 19.1.2012Quintessentially English - scenes from our Wiltshire townPython - current versions and implementations (CPython, Jython, IronPython etc)