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Collections in Python - list tuple dict and string.

All the languages that we teach have "collection" variables - single names under which a series of values is stored, keyed or indexed in some way. There are four such types in Python

Lists ... starting off with index position 0, and alterable within the stucture as the program runs. You may erroneously associate such a structure with the word "array" - technically incorrect because an array is usually at successive memory loactions, whereas a list isn't necessarily so. At the cost of a little speed in simple operations, the structure of a list allows it to be extended once it's been created, and allows elements to be removed from and inserted into the middle without having to move up all the rest of the data.

Tuples ... also indexed from position 0, but NOT alterable within the stucture as the program runs. If you want to change a tuple, you have to get rebuild and replace the whole collection - quite straightforward, but inefficient. On the other hand, if you set up data in a single statement and then don't want to change it, a tuple gives you a speed advantage.

Dicts ... keyed by name / object rather than by position number. Dicts are sometimes compared to database tables with two columns (a key and value), and at other times to PHP's associative array, or to hashes in Perl. That last's probably the closest comparison and dicts are defined for very fast access to data via keys, at the expense of not being sortable.

Strings ... are a collection of characters. Like Tuples, once set up you're required to rebuild the whole of a string if you change it.

You can create any of these variables (objects) using its constructor, or use shorthands if you prefer:
  [] for list
  {} for dict
  () for tuple
  "" for string (or '' or triple quotes)
and you can then reference individual elements within any of the collections using [].

Examples of all the syntax - [here] - my demonstration from last week's Python training class.
(written 2013-03-04)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y104 - Python - Lists and Tuples
  [4722] Embedding more complex code into a named block - (2016-11-04)
  [4368] Shuffling a list - Ruby and Python - (2014-12-28)
  [3763] Spike solutions and refactoring - a Python example - (2012-06-13)
  [3669] Stepping through a list (or an array) in reverse order - (2012-03-23)
  [3348] List slices in Python - 2 and 3 values forms, with an uplifting example - (2011-07-06)
  [3257] All possible combinations from a list (Python) or array (Ruby) - (2011-04-23)
  [3181] Beware - a=a+b and a+=b are different - Python - (2011-02-23)
  [3118] Arrays of arrays - or 2D arrays. How to program tables. - (2011-01-02)
  [2996] Copying - duplicating data, or just adding a name? Perl and Python compared - (2010-10-12)
  [2719] Traffic lights in Python - (2010-04-13)
  [2368] Python - fresh examples of all the fundamentals - (2009-08-20)
  [2284] Strings as collections in Python - (2009-07-12)
  [2280] Creating and iterating through Python lists - (2009-07-12)
  [1789] Looking for a value in a list - Python - (2008-09-08)
  [1641] Tektronix 4010 series / Python Tuples - (2008-05-13)
  [1220] for loop - how it works (Perl, PHP, Java, C, etc) - (2007-06-06)
  [955] Python collections - mutable and imutable - (2006-11-29)
  [899] Python - extend v append on a list - (2006-10-20)
  [657] The ternary operator in Python - (2006-03-25)
  [383] Overloading of operators on standard objects in Python - (2005-07-19)

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)
  [4409] Setting up and using a dict in Python - simple first example - (2015-01-30)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (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)
  [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)
  [103] Can't resist writing about Python - (2004-10-29)

Y108 - Python - String Handling
  [4659] Prining a pound sign from Python AND running from the command line at the same time - (2016-03-03)
  [4595] Python formatting update - including named completions - (2015-12-10)
  [4593] Command line parameter handling in Python via the argparse module - (2015-12-08)
  [4360] Python - comparison of old and new string formatters - (2014-12-22)
  [4307] Identifying and clearing denial of service attacks on your Apache server - (2014-09-27)
  [4213] Formatting options in Python - (2013-11-16)
  [4152] Why are bus fares so high? - (2013-08-18)
  [3886] Formatting output - why we need to, and first Python example - (2012-10-09)
  [3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [3468] Python string formatting - the move from % to str.format - (2011-10-08)
  [3349] Formatting output in Python through str.format - (2011-07-07)
  [3218] Matching a license plate or product code - Regular Expressions - (2011-03-28)
  [3090] Matching to a string - what if it matches in many possible ways? - (2010-12-17)
  [2814] Python - splitting and joining strings - (2010-06-16)
  [2780] Formatted Printing in Python - (2010-05-25)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2692] Flexible search and replace in Python - (2010-03-25)
  [2406] Pound Sign in Python Program - (2009-09-15)
  [1876] Python Regular Expressions - (2008-11-08)
  [1608] Underlining in Perl and Python - the x and * operator in use - (2008-04-12)
  [1517] Python - formatting objects - (2008-01-24)
  [1195] Regular Express Primer - (2007-05-20)
  [1110] Python - two different splits - (2007-03-15)
  [970] String duplication - x in Perl, * in Python and Ruby - (2006-12-07)
  [954] Splitting Pythons in Bradford - (2006-11-29)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [903] Pieces of Python - (2006-10-23)
  [773] Breaking bread - (2006-06-22)
  [560] The fencepost problem - (2006-01-10)
  [496] Python printf - (2005-11-15)
  [463] Splitting the difference - (2005-10-13)
  [324] The backtick operator in Python and Perl - (2005-05-25)


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Really Simple Class and Inheritance example in Python
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