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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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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))
Python - how it saves on compile time

Python is interpreted every time you run the code ... or that's the simple first story you're told. But really it's not that simple ... and not that inefficient.

When you run a Python program, it is not interpreted line by line as you run it - it is interpreted all at once before it's run at all, and stored as "byte code" so that loops and methods don't need to be re-interpreted hundreds or thousands of times during a single execution ... the Python virtual machine (for that's what it is) simply comes back to the already-worked-out store.

It gets even more efficient when you come to modules that you load through from or import. Their virtual machine code is saves into files with the extension .pyc (or .pyo if you use the optimize option) and they are loaded directly without the need to recompile on future runs. A quick operating system check on file time stamps means that if you change your source file, it will be 'silently' recompiled and resaved.

Other languages which are described as 'scripting' languages use a similar technique. See here, for example, to see how Lua does it.
(written 2009-10-20)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y305 - Optimising Python
  [2277] Python classes / courses - what version do we train on? - (2009-07-10)
  [2369] Using a cache for efficiency. Python and PHP examples - (2009-08-21)
  [3766] Python timing - when to use a list, and when to use a generator - (2012-06-16)
  [4088] Some tips and techniques for huge data handling in Python - (2013-05-15)

Y115 - Additional Python Facilities
  [183] The elegance of Python - (2005-01-19)
  [208] Examples - Gadfly, NI Number, and Tcl to C interface - (2005-02-10)
  [239] What and why for the epoch - (2005-03-08)
  [463] Splitting the difference - (2005-10-13)
  [663] Python to MySQL - (2006-03-31)
  [672] Keeping your regular expressions simple - (2006-04-05)
  [753] Python 3000 - the next generation - (2006-06-09)
  [901] Python - listing out the contents of all variables - (2006-10-21)
  [1043] Sending an email from Python - (2007-01-18)
  [1136] Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP - (2007-04-06)
  [1149] Turning objects into something you can store - Pickling (Python) - (2007-04-15)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1337] A series of tyre damages - (2007-09-08)
  [1876] Python Regular Expressions - (2008-11-08)
  [2407] Testing code in Python - doctest, unittest and others - (2009-09-16)
  [2435] Serialization - storing and reloading objects - (2009-10-04)
  [2655] Python - what is going on around me? - (2010-02-28)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2745] Connecting Python to sqlite and MySQL databases - (2010-04-28)
  [2746] Model - View - Controller demo, Sqlite - Python 3 - Qt4 - (2010-04-29)
  [2764] Python decorators - your own, staticmethod and classmethod - (2010-05-14)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2786] Factory methods and SqLite in use in a Python teaching example - (2010-05-29)
  [2790] Joining a MySQL table from within a Python program - (2010-06-02)
  [3089] Python regular expressions - repeating, splitting, lookahead and lookbehind - (2010-12-17)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [4085] JSON from Python - first principles, easy example - (2013-05-13)
  [4211] Handling JSON in Python (and a csv, marshall and pickle comparison) - (2013-11-16)
  [4298] Python - an interesting application - (2014-09-18)
  [4439] Json is the new marshall, pickle and cPickle / Python - (2015-02-22)
  [4451] Running an operating system command from your Python program - the new way with the subprocess module - (2015-03-06)
  [4536] Json load from URL, recursive display, Python 3.4 - (2015-10-14)
  [4593] Command line parameter handling in Python via the argparse module - (2015-12-08)
  [4709] Some gems from Intermediate Python - (2016-10-30)


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Tcl - a true interpretive, command based language
Some other Articles
Tcl - passing arrays and strings in and back out of procs
Melksham Town - asleep or awake?
Beauty in pictures
Tcl - a true interpretive, command based language
Python - how it saves on compile time
Luac - getting lua to start fast by precompiling
Mothers Day or Mothering Sunday?
New Web Site for Melksham Chamber of Commerce
Cant connect to local MySQL server through socket /tmp/mysql.sock
Railway Arithmetic
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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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