Some more new examples in Python - from this week's course.

From my Introduction to Python / simple example to show the power of the language, I present my example that parsed a big data (log) file and counter and sorted by number of accesses the hits from various remote hosts. A long report, ending as follows:
216.129.119.10 549
216.129.119.44 580
66.249.71.164 587
66.249.68.89 2975
217.160.182.81 3215
72.30.142.107 3250
77.88.28.246 4815
66.249.71.55 5457
Dorothy-2:p2 grahamellis$
With the program source available [here].

The some shorter / easier stuff from the first day:

An program to provide a chart of exchange rates - the sort you would give your children when you take them overseas and want to teach them about the local money, and have them work out what is good value. [here].

A short example of how to save a multiline string in a variable in Python. [here].

A prompt ... read ... calculate ... report program in Python. [here].

In Python, you can save yourself writing loops to go through each element of a list by using list methods and operators. We wrote a 'control' example showing how it would work in any language [here], and went on to reduce the looping dramatically [here]. In both cases, the programs produce two lists of 365 elements - representing days of the year. One list has 31 1s, 28 2s and so on - to convert day of year to month of year, and the other list has the numbers 1 to 31, then 1 to 28, and so on, to convert day of year to day of month.

Newcomers often get confused between assigning to the whole of a list (replacing the whole thing) and assigning to an element (replacing just that element and leaving the rest in tact. Our final first day example - [here] illustrates both in source code, with
listname = replacing the whole list and
listname[6] = replacing just the 7th element.

Examples from the second day

Functions, Modules, Packages, and Object Orientation in Python!

In most languages, functions run to completion before they return anything, but in Python you can write a generator which passes back a series of values at yield statements - thus providing an iterator. This is especially useful where you have a big data set - you don't have to read the whole dataset into memory in one go and then process it bit by bit, nor have the read and process in one function. We wrote a 'control' case [here] showing how this would be in a conventional language, and then did it the python way with a generator [here]. You can do this in Lua - using coroutines - too.

The map function converts every member of a list through a function which you pass in as a parameter, and the filter function return you a list of (only) matching itemes, as identified by a callback function in the call. Consider these to be the equivalents of map and grep in Perl if you like ... and see the example source code [here].

As programs grow, you need to separate out your variables into different namespaces - you need to be able to tell "John Smith" from "John Jones" so in Python, you write smith.john of jones.john. And you load namespaces from different files. Example - the file that does the loading [here], and the file it loaded [here] - that latter complete with its own test code to allow you to check it works on its own before integrating it with your main code.

In Java, defining and using a class would be 2 separate files with lots of "public"s and "private"s. And in C++ you would have half a dozen files. Which is why Python's OO model is so sweet - the whole thing can be done in one file - and we have an example [here]. We also have an example with a static (class) variable [here] and we even have examples with multiple classes - look forward to day 3, but they're still potentially all in the one file if they're going to be coded, used and maintained in tandem.

Day 3 - a bit beyond the basics

Some string handling and formatting - [here] is the use of the % operator both for modulo (integer) and formatting - the operator is overloaded - and a regular expression example which shows you how you can split a string at either an exact match, or at a pattern - [here].

Polymorphism and Inheritance - the way data types can all be defined from the same starting point, with only the differences being coded, and then how those subtley different objects can automatically behave in the way designated for them - comes naturally in Python. We have examples [here] which show multiple related classes, and comparators, and [here] showing how they can be wrapped into a module.

Regular expressions ... we cover quite a lot there ... included a new example [here] where I looked for all the postcodes in a string.
(written 2009-08-20, updated 2009-08-23)

 Y303 - Python Network Programming
  [2365] Counting Words in Python via the web - (2009-08-18)
  [2694] Multiple processes (forking) in Python - (2010-03-25)
  [2695] TCP v UDP / Client v Server - Python examples - (2010-03-25)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [4087] Python network programming - new FTP and socket level examples - (2013-05-14)

Y112 - Python - Objects - Intermediate
  [296] Using a Python dictionary as a holder of object attributes - (2005-04-30)
  [383] Overloading of operators on standard objects in Python - (2005-07-19)
  [477] Class, static and unbound variables - (2005-10-25)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [903] Pieces of Python - (2006-10-23)
  [964] Practical polymorphism in action - (2006-12-04)
  [1146] __new__ v __init__ - python constructor alternatives? - (2007-04-14)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [1517] Python - formatting objects - (2008-01-24)
  [1644] Using a utility method to construct objects of different types - Python - (2008-05-17)
  [1661] Equality, sameness and identity - Python - (2008-05-31)
  [1819] Calling base class constructors - (2008-10-03)
  [2409] TypeError: super() argument 1 must be type, not classobj (Python) - (2009-09-18)
  [2485] How do I set up a constant in Python? - (2009-10-31)
  [2693] Methods that run on classes (static methods) in Python - (2010-03-25)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2720] Multiple inheritance in Python - complete working example - (2010-04-14)
  [2722] Mixins example in Python - (2010-04-14)
  [2764] Python decorators - your own, staticmethod and classmethod - (2010-05-14)
  [2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
  [2889] Should Python classes each be in their own file? - (2010-07-27)
  [2905] Defining static methods in Python - (2010-08-05)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [3002] A list of special method and attribute names in Python - (2010-10-17)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [3472] Static variables in functions - and better ways using objects - (2011-10-10)
  [3524] Metaclasses (Python) and Metatables (Lua) - (2011-11-17)
  [3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
  [3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
  [4028] Really Simple Class and Inheritance example in Python - (2013-03-04)
  [4094] Python Properties - how and why - (2013-05-18)
  [4344] Python base and inherited classes, test harness and unit testing - new examples - (2014-12-07)
  [4356] Object factories in C++, Python, PHP and Perl - (2014-12-19)
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [4410] A good example of recursion - a real use in Python - (2015-02-01)
  [4449] Spike solution, refactoring into encapsulated object methods - good design practise - (2015-03-05)
  [4450] Deciding whether to use parameters, conditional statements or subclasses - (2015-03-05)
  [4541] Setting up and tearing down with the Python with keyword - (2015-10-16)
  [4649] Object and Static methods - what is the difference; example in Python 3 - (2016-02-17)
  [4717] with in Python - examples of use, and of defining your own context - (2016-11-02)
  [4718] Defining an object that is a modified standard type in Python - (2016-11-02)
  [4719] Nesting decorators - (2016-11-02)

Y109 - Python - Exceptions
  [381] Exceptions in Python - (2005-07-17)
  [1042] Nested exceptions in Python - (2007-01-18)
  [1236] Trying things in Python - (2007-06-18)
  [2018] UnboundLocalError - Python Message - (2009-01-31)
  [2281] Python - using exceptions to set a fallback - (2009-07-12)
  [2408] Robust user input (exception handling) example in Python - (2009-09-17)
  [2622] Handling unusual and error conditions - exceptions - (2010-02-03)
  [2998] Using an exception to initialise a static variable in a Python function / method - (2010-10-13)
  [3177] Insurance against any errors - Volcanoes and Python - (2011-02-19)
  [3433] Exceptions - a fail-safe way of trapping things that may go wrong - (2011-09-11)
  [3441] Pressing ^C in a Python program. Also Progress Bar. - (2011-09-15)
  [3664] Error checking in a Python program - making your program robust via exceptions - (2012-03-22)
  [3913] How many times ... has this loco headed west through Tenby? - Python exceptions - (2012-11-05)
  [3930] Reporting the full stack trace when you catch a Python exception - (2012-11-22)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04)
  [4161] Python varables - checking existance, and call by name or by value? - (2013-08-27)
  [4444] Elements of an exception in Python - try, except, else, finally - (2015-02-28)

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)
  [2915] Looking up a value by key - associative arrays / Hashes / Dictionaries - (2010-08-11)
  [2986] Python dictionaries - reaching to new uses - (2010-10-05)
  [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)
  [4409] Setting up and using a dict in Python - simple first example - (2015-01-30)
  [4469] Sorting in Python 3 - and how it differs from Python 2 sorting - (2015-04-20)
  [4661] Unique word locator - Python dict example - (2016-03-06)
  [4668] Sorting a dict in Python - (2016-04-01)

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

Y102 - Python - Fundamentals
  [328] Making programs easy for any user to start - (2005-05-29)
  [633] Copying a reference, or cloning - (2006-03-05)
  [748] Getting rid of variables after you have finished with them - (2006-06-06)
  [956] Python security - trouble with input - (2006-11-30)
  [1430] Integer v float - Python - (2007-11-12)
  [1448] Question on division (Java) - Also Perl, PHP, Python ... - (2007-11-28)
  [1461] Python - input v raw input - (2007-12-06)
  [1878] Pascals Triangle in Python and Java - (2008-11-10)
  [2442] Variable storage - Perl, Tcl and Python compared - (2009-10-08)
  [2778] Learning to program in Python 2 ... and / or in Python 3 - (2010-05-24)
  [3083] Python - fresh examples from recent courses - (2010-12-11)
  [3278] Do I need to initialise variables - programming in C, C++, Perl, PHP, Python, Ruby or Java. - (2011-05-05)
  [3551] Some terms used in programming (Biased towards Python) - (2011-12-12)
  [3886] Formatting output - why we need to, and first Python example - (2012-10-09)
  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
  [4324] Learning to program - variables and constants - (2014-11-22)
  [4442] Mutable v Immuatble objects in Python, and the implication - (2015-02-24)
  [4712] A reminder of the key issues to consider in moving from Python 2 to Python 3 - (2016-10-30)

Back to Learning to program - how to jump the first hurdles

Previous and next or Horse's mouth home

Forward to Using a cache for efficiency. Python and PHP examples

Public Transport from (and to) Melksham on Sundays
Quiet summer days? I think not!
C++, Python, and other training - do we use an IDE
Using a cache for efficiency. Python and PHP examples
Python - fresh examples of all the fundamentals
Learning to program - how to jump the first hurdles
At the end of the course
Getting it right from the start - new programmers
Alpaca Case or Camel Case