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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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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))
Sorting in Python 3 - and how it differs from Python 2 sorting

Sorting has changed between Python 2 and Python 3 ... and it's easy and logical to sort lists in Python 3. Problem is that the Python 3 documentation shows you really complicated examples ...

There are two ways of sorting a list in Python 3:
a) You can use the sorted function, into which you pass a list; it returns an ordered list.
b) You can use the sort method on a list, in which case the list is modified in situ.

By default, both sort and sorted re-order elements in their "natural" order, running the cmp function on the elements of the list being compared. So if you're sorting your own objects, you can redefine __cmp__ to change that sort order.

In Python 3, just as in Python 2, you can't sort a dict / dictionary. It uses a hashing technique for quick access to elements in a large collection, and such a technique is simply incompatible with sorting (come on Python Course and I'll explain why!). But you can sort a list of keys.

Here's an example of sorting a list of keys (by the key):
  towns = sorted(list(counties.keys()))
  for town in towns:

and an alternative sorting by values - passing in a key function to tell it how to sort:
  towns = sorted(list(counties.keys()),key=lambda x:counties[x])
  for town in towns:

Complete example code [here]

If you prefer to sort a list in situ, by key:
  towns = list(counties.keys())
  towns.sort()

  for town in towns:
and by value:
  towns = list(counties.keys())
  towns.sort(key=lambda x:counties[x])
  for town in towns:

Complete example code [here]

If you're using Python 2, you'll find an equivalent piece of code [here]. It's descibed as being "Python 2.7" because it makes use of the str.format method's enhancements that were added at that release.
(written 2015-04-20, updated 2015-04-22)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y300 - Python 3 - What is new, what's changed and why
  [753] Python 3000 - the next generation - (2006-06-09)
  [1788] Python 2 to Python 3 / Python 3000 / Py3k - (2008-09-07)
  [1791] The road ahead - Python 3 - (2008-09-10)
  [2277] Python classes / courses - what version do we train on? - (2009-07-10)
  [2285] Great new diagrams for our notes ... Python releases - (2009-07-13)
  [2559] Moving the product forward - ours, and MySQL, Perl, PHP and Python too - (2010-01-01)
  [2778] Learning to program in Python 2 ... and / or in Python 3 - (2010-05-24)
  [2871] Moving from Python 2.6 to Python 3 - (2010-07-14)
  [4470] Testing in Python 3 - unittest, doctest and __name__ == __main__ too. - (2015-04-21)
  [4590] Progress on moving from Python 2 to Python 3 - training for both versions - (2015-12-01)
  [4649] Object and Static methods - what is the difference; example in Python 3 - (2016-02-17)
  [4650] Why populate object with values as you construct them? - (2016-02-18)
  [4711] Convering from Python 2 to Python 3 - an update, and the 2to3 utility - (2016-10-30)
  [4712] A reminder of the key issues to consider in moving from Python 2 to Python 3 - (2016-10-30)

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)
  [3464] Passing optional and named parameters to python methods - (2011-10-04)
  [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)
  [4661] Unique word locator - Python dict example - (2016-03-06)
  [4668] Sorting a dict in Python - (2016-04-01)


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or
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Forward to
Testing in Python 3 - unittest, doctest and __name__ == __main__ too.
Some other Articles
Fishguard to Melksham - third part of Dublin journey
Rosslare to Fishguard - foot passenger on the ferry
Leopardstown to Rosslare by train
Sorting in Python 3 - and how it differs from Python 2 sorting
Four in a Bed - most popular answers
Neighbourhood Plan - travel and transport thoughts
Moving from C to C++ - Structured to Object Oriented - a lesson for engineers
Sockets, time handling and keyboard interrupt handling in C
Catching up on a week all in a single post (?)
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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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