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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.
Identity in Python

There's a differece between "the same", "equal" and "identical". I can have two identical 5p coins, but they're not the same coin. And I can have two coins which are not identical, but are equal in value. And when you're checking for equality in a program, you should know which you're looking at. Take a look at this in Python:

  >>> a = [10]
  >>> b = [10]
  >>> c = a
  >>> a == b
  True
  >>> a is b
  False
  >>> a is c
  True
  >>>


a and b are different lists, but they contain identical information. c is another name for the list which is also called a.

The == operator tells you whether two variables (or expressions) contain equal values, whether or not they're the same actual object.

The is operator tells you whether two variable names point to the same object.

A list (as used above) is a mutable object - something that can be changed within itself. Integers, floats, strings and tuples are immutable - in other words if you want to change something, you need to create a new replacement object. And in Python, identical immutable objects are stored only once for efficiency - so you'll find a different set of results from using is ... if two immutable objects are identical, they'll be the same object. Thus:

  >>> a = 10
  >>> b = 10
  >>> c = a
  >>> a == b
  True
  >>> a is b
  True
  >>> a is c
  True
  >>>

(written 2013-05-17, updated 2013-05-18)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y103 - Python - Conditionals and Loops
  [299] What - no switch or case statement? - (2005-05-03)
  [353] Wimbledon Neck - (2005-06-20)
  [657] The ternary operator in Python - (2006-03-25)
  [668] Python - block insets help with documentation - (2006-04-04)
  [788] New - Conditional expressions in Python 2.5 - (2006-07-01)
  [835] Python - when to use the in operator - (2006-08-16)
  [909] Python is like a narrowboat - (2006-10-30)
  [1201] No switch in Python - (2007-05-23)
  [1477] Decisions - small ones, or big ones? - (2007-12-18)
  [1661] Equality, sameness and identity - Python - (2008-05-31)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [2778] Learning to program in Python 2 ... and / or in Python 3 - (2010-05-24)
  [2899] Groupsave tickets - 3 or 4 train tickets for the price of 2 - (2010-08-02)
  [3083] Python - fresh examples from recent courses - (2010-12-11)
  [3200] How a for loop works Java, Perl and other languages - (2011-03-12)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3439] Python for loops - applying a temporary second name to the same object - (2011-09-14)
  [3558] Python or Lua - which should I use / learn? - (2011-12-21)
  [3620] Finding the total, average, minimum and maximum in a program - (2012-02-22)
  [3762] Learning to program - the if statement. Python. - (2012-06-12)
  [3895] Flowchart to program - learning to program with Well House - (2012-10-14)
  [4210] If elif elif elif - multiway selection in Python - (2013-11-16)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4402] Finding sum, minimum, maximum and average in Python (and Ruby) - (2015-01-19)
  [4541] Setting up and tearing down with the Python with keyword - (2015-10-16)
  [4545] Method, Class, Module, Package - how to they relate in Python? - (2015-10-17)
  [4713] Equality (in Python) - (2016-10-30)
  [4723] Conditional operators in Python - (2016-11-05)


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More things to make sure that we do NOT do ...
Some other Articles
Perl design patterns example
Django - first steps - Updated
Python Properties - how and why
More things to make sure that we do NOT do ...
Identity in Python
A reminder of why we opened Well House Manor for our customers
Test Driven Development in Python - Customer Comes First
Quick and easy - showing Python data hander output via a browser
Some tips and techniques for huge data handling in Python
Python network programming - new FTP and socket level examples
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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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