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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.
Lazy operators in Lua - what they mean, and examples

If you use the word or in an expression in Lua, the expression to the right of the word will only be evaluated and returned of the value to the left is nil. So a very common idiom is:
  stuff = stuff or {}
which means "if stuff already has a value, leave it alone - otherwise make it an empty table"

If you use the word and on the other hand, the expression to the right of the word will only be evaluated nd returned if the value to the left is not nil. This is a much less common requirement:
  stuff = stuff and {}
which means "if stuff has a value, replace it with an empty table. But if it's nil, leave it like that"

Example from the Lua course completed at the end of last week - [here] and another example from earlier on [here].

(written 2014-05-05, updated 2014-05-06)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
U103 - Lua - Conditionals and loops
  [1685] Short circuit evaluation (lazy operator) in Lua - (2008-06-22)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1738] Clean code, jump free (Example in Lua) - (2008-08-06)
  [2351] Ternary operators alternatives - Perl and Lua lazy operators - (2009-08-12)
  [2454] For loops in Lua - (2009-10-14)
  [2455] Lua examples - coroutines, error handling, objects, etc - (2009-10-15)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3558] Python or Lua - which should I use / learn? - (2011-12-21)
  [3686] The goto statement in Lua - (2012-04-06)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4574] repeat until in Lua - a one or more rather than a zero or more loop - (2015-11-05)


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Lazy operators in Lua - what they mean, and examples
Line, block and nested comments - Lua compared to other languages
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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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