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Some gems from an introduction to Python

This week, I ran a private Introduction to Python course - using Python 2.7 at customer request - and here are some of the code snippets I wrote in front of the class - little things I may not have blogged about in the past. Complete examples being emailed to the delegates!

 # Using an exception to see in an object exists (in this case within a dict)
 # --------------------------------------------------------------------------
 
         try:
                 counter[website] += 1
         except KeyError,e:
                 counter[website] = 1
                 print e
 
 # sorting and printing by value
 # -----------------------------
 
 def byvalue(that,this):
         return cmp(counter[this],counter[that])
 
 domains = counter.keys()
 domains.sort(byvalue)
 
 for d in domains:
         print "%-8d %s" % (counter[d],d)
 
 # printing documentation within a test harness
 # --------------------------------------------
 
 if __name__ == "__main__":
         # (main test code here)
         print
         print person.__doc__
 
 # printing with old and new formatters
 # ------------------------------------
 
 print "%8.2f is the value for %-7s today" % (people[person],person)
 print "{0:8.2f} is the value for {1:<7s} today".format(people[person],person)
 
 # How to unwrap a collection into a function
 # ------------------------------------------
 
 sz = (12,16)
 # print getArea(sz[0],sz[1]) ; this is the long-winded way!
 print getArea(*sz)
 
 # decorator ... new and old ways
 # ------------------------------
 
         @staticmethod
         def factory(raw):
                 # code
                 return product
         # decorator at top of method does the following:
         # factory = staticmethod(factory)
 
 # generator ... and list code as comments
 # ---------------------------------------
 
 def places():
         # small = []
         for lyne in fh.xreadlines():
                  (code on line)
                  # small.append(fol[6])
                  print "splash"
                  yield fol[6]
         # return small
 
 # functions that take different parameter patterns
 # ------------------------------------------------
 
 def myrange(*inputs):
         # passed a list
         if isinstance(inputs[0],list):
                 inputs = inputs[0]
         # passed three params
         if len(inputs) == 3:
                 etc
 
 # variety of regular expressions to match a postcode
 # --------------------------------------------------
 
 poco = re.compile(r'[A-Z]{1,2}[0-9]{1,2} {1,}[0-9]{1}[A-Z]{2}')
 poco = re.compile(r'(([A-Z]{1,2})[0-9]{1,2}) {1,}([0-9]{1}[A-Z]{2})')
 poco = re.compile(r'(([A-Z]{1,2})[0-9]{1,2}) {1,}([0-9]{1}[A-Z]{2})$')
 poco = re.compile(r'(([A-Z]{1,2})\d[A-Z0-9]?)\s+([0-9][A-Z]{2})',re.IGNORECASE)
 
 
 # static variable in a function
 # -----------------------------
 
 def more():
         print "dot"
         try:
                 more.keep += 1
         except:
                 more.keep = 1
         print more.keep
 
 # lazy operator, python style with and and or
 # -------------------------------------------
 
 def getNet(amount,vset=None):
         # vatrate is an external (fallback) variable
         vr = (vset == None) and vatrate or vset
 
 
 # using a slice on a string
 # -------------------------
 
 uat = sample.find("u")
 sat = sample.find(" ",uat)
 print sample[uat:sat]

(written 2016-10-29)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y199 - Python - Fast Start
  [4713] Equality (in Python) - (2016-10-30)
  [4712] A reminder of the key issues to consider in moving from Python 2 to Python 3 - (2016-10-30)
  [4709] Some gems from Intermediate Python - (2016-10-30)
  [3519] Python - current versions and implementations (CPython, Jython, IronPython etc) - (2011-11-13)
  [2017] Python - a truly dynamic language - (2009-01-30)

Q110 - Object Orientation and General technical topics - Programming Algorithms
  [4656] Identifying the first and last records in a sequence - (2016-02-26)
  [4652] Testing new algorithms in PHP - (2016-02-20)
  [4410] A good example of recursion - a real use in Python - (2015-02-01)
  [4402] Finding sum, minimum, maximum and average in Python (and Ruby) - (2015-01-19)
  [4401] Selecting RECENT and POPULAR news and trends for your web site users - (2015-01-19)
  [4325] Learning to program - what are algorithms and design patterns? - (2014-11-22)
  [3662] Finding all the unique lines in a file, using Python or Perl - (2012-03-20)
  [3620] Finding the total, average, minimum and maximum in a program - (2012-02-22)
  [3451] Why would you want to use a Perl hash? - (2011-09-20)
  [3102] AND and OR operators - what is the difference between logical and bitwise varieties? - (2010-12-24)
  [3093] How many toilet rolls - hotel inventory and useage - (2010-12-18)
  [3072] Finding elements common to many lists / arrays - (2010-11-26)
  [3042] Least Common Ancestor - what is it, and a Least Common Ancestor algorithm implemented in Perl - (2010-11-11)
  [2993] Arrays v Lists - what is the difference, why use one or the other - (2010-10-10)
  [2951] Lots of way of converting 3 letter month abbreviations to numbers - (2010-09-10)
  [2894] Sorting people by their names - (2010-07-29)
  [2617] Comparing floating point numbers - a word of caution and a solution - (2010-02-01)
  [2586] And and Or illustrated by locks - (2010-01-17)
  [2509] A life lesson from the accuracy of numbers in Excel and Lua - (2009-11-21)
  [2259] Grouping rows for a summary report - MySQL and PHP - (2009-06-27)
  [2189] Matching disparate referencing systems (MediaWiki, PHP, also Tcl) - (2009-05-19)
  [1949] Nuclear Physics comes to our web site - (2008-12-17)
  [1840] Validating Credit Card Numbers - (2008-10-14)
  [1391] Ordnance Survey Grid Reference to Latitude / Longitude - (2007-10-14)
  [1187] Updating a page strictly every minute (PHP, Perl) - (2007-05-14)
  [1157] Speed Networking - a great evening and how we arranged it - (2007-04-21)
  [642] How similar are two words - (2006-03-11)
  [227] Bellringing and Programming and Objects and Perl - (2005-02-25)
  [202] Searching for numbers - (2005-02-04)


Back to
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or
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Forward to
Scons - a build system in Python - building hello world
Some other Articles
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
Scons - a build system in Python - building hello world
Some gems from an introduction to Python
Melksham trial train service is to be made permanent
Course dates - from October 2016 to December 2017
Three months in community rail pictures
What do people use the bus for in Wiltshire - survey interim results.
Up and down TransWilts - some pictures off the rails!
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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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