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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.
Searching a Json or XML structure for a specific key / value pair in Python

With data loaded from JSon or XML structures, you'll often want to search for attributes by element name - without having to code the structure, and with the code adapting itself to mean subtle structure changes in the suppied data.

Here's an example written during lat week's tailored Intermediate Python course ... taking a Json object (loaded from our web resource) and displaying a list of all the elements of a specific name.

As good python code encapsulate all the hard work into methods, our main progam is very short.

If I want to find the value of all the fields keyed "where" ... Loading the data

  fh = open("jflow.json")
  igot = json.load(fh)
  found = parseDict(igot,"where")


and the hard work is done in parseDict as json.load returns a dict. parseDict has been written to return a list.

Sorting the results:

  if sys.version_info < (3,0):
    found.sort(lambda x,y:cmp(len(x),len(y)))
  else:
    found.sort(key = lambda x:len(x))


and displaying the results, 4 per line.

  print("Here are the remote IP visitors to your images")
  for k in range(len(found)):
    sep = ((k+1)%4 and k+1 != len(found)) and " " or "\n"
    sys.stdout.write("%16s%s"%(found[k],sep))


Full source code is [here] . The data ('pretty printed' as Json compressed is hard to read!) is [here]

parseDict is a piece of recursive code - two re-entrant pieces of code which call each other as they traverse your structure and find lists and dicts within other lists and dicts. I am not normally a fan of recursive / re-entrant code on courses, as they're typically over-clever solutions looking for problems, but this particular use is sensible.

I'll cover this for you on Python Intermediate courses or on Python Programming courses (in that case after class hours if you make a specific request, as not everyone wants to do this).
(written 2016-10-30)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y151 - Python & XML
  [2378] Handling XML in Perl - introduction and early examples - (2009-08-27)
  [2506] Good example of recursion in Python - analyse an RSS feed - (2009-11-18)
  [2555] Bookkeeping - (2009-12-29)
  [3082] XML handling in Python - SAX, DOM and XSLT examples - (2010-12-09)
  [4594] XML handling in Python - a new teaching example using etree - (2015-12-09)

Y117 - Python - Already written modules
  [2020] Learning Python - many new example programs - (2009-01-31)
  [2890] Dates and times in Python - (2010-07-27)
  [2931] Syncronise - software, trains, and buses. Please! - (2010-08-22)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [3465] How can I do an FTP transfer in Python? - (2011-10-05)
  [3479] Practical Extraction and Reporting - using Python and Extreme Programming - (2011-10-14)
  [4085] JSON from Python - first principles, easy example - (2013-05-13)
  [4086] Cacheing class for Python - using a local SQLite database as a key/value store - (2013-05-14)
  [4441] Reading command line parameters in Python - (2015-02-23)
  [4452] Binary data handling - Python and Perl - (2015-03-09)
  [4696] Programming with random numbers - yet re-using the same values for testing - (2016-06-22)
  [4697] Month, Day, Year number to day of week and month names in Python - English and Swedish - (2016-06-23)
  [4708] Scons - a build system in Python - building hello world - (2016-10-29)


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Equality (in Python)
A reminder of the key issues to consider in moving from Python 2 to Python 3
Convering from Python 2 to Python 3 - an update, and the 2to3 utility
Searching a Json or XML structure for a specific key / value pair in Python
Some gems from Intermediate Python
Some gems from an introduction to Python
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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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