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Setting up and using a dict in Python - simple first example

Here's a very short and easy example of the use of a dict in Python.

Set up a dict and fill it from a file (key value is 2nd field; value to be looked at is 7th)

  lookup = {}
  for record in open("railstats.txt","r"):
    fields = record.strip().split('\t')
    tlc = fields[1]
    name = fields[6]
    lookup[tlc] = name


You can't sort a dict - but you CAN sort a list of the keys

  codes = lookup.keys()
  codes.sort(lambda a,b: cmp(lookup[b],lookup[a]))


And you can then list the elements in the order of the list

  for code in codes:
    print code,lookup[code])


Complete code [here].

It's all very well looking at what a program does - but would you know how to decide how to write it like this? Our Pyton Programming courses will teach you. Follow our course schedule link if you'ld like to come - at the time of writing, I'm actually presenting a private course, there's another private course at the end of next month (February) and then there's a public course starting on 2nd March 2015, but the diary is updated if you've found this page on our archive, and we have dates available (from mid March) for private courses.
(written 2015-01-30)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y107 - Python - Dictionaries
  [4668] Sorting a dict in Python - (2016-04-01)
  [4661] Unique word locator - Python dict example - (2016-03-06)
  [4469] Sorting in Python 3 - and how it differs from Python 2 sorting - (2015-04-20)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04)
  [4027] Collections in Python - list tuple dict and string. - (2013-03-04)
  [3934] Multiple identical keys in a Python dict - yes, you can! - (2012-11-24)
  [3662] Finding all the unique lines in a file, using Python or Perl - (2012-03-20)
  [3555] Football league tables - under old and new point system. Python program. - (2011-12-18)
  [3554] Learning more about our web site - and learning how to learn about yours - (2011-12-17)
  [3488] Python sets and frozensets - what are they? - (2011-10-20)
  [3464] Passing optional and named parameters to python methods - (2011-10-04)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [2986] Python dictionaries - reaching to new uses - (2010-10-05)
  [2915] Looking up a value by key - associative arrays / Hashes / Dictionaries - (2010-08-11)
  [2368] Python - fresh examples of all the fundamentals - (2009-08-20)
  [1145] Using a list of keys and a list of values to make a dictionary in Python - zip - (2007-04-13)
  [1144] Python dictionary for quick look ups - (2007-04-12)
  [955] Python collections - mutable and imutable - (2006-11-29)
  [103] Can't resist writing about Python - (2004-10-29)


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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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