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When to check an object type - Python isinstance example
I'll encourage you not
to look at an object in a Python program - or in any other OO langauge - you find out what type it is ... at least until you've thought about why you're doing it.
If you need to, you can look - you have the type
function, you have the __class__.__name__
variable and you have isinstance
Isinstance lets you check the hierarcy of an object - so I can use it to ask if an object is of a particular type, or a type that's based on it.
Here's a look to see if something's a list:
and in use in a program [here]
. I'm not thrilled with the example - but is shows you the syntax. I would much rather you used polymorphism (several methods of the same name in order to decide internally how to print the data) rather than a branch chain based on the type.
Where I will
encourage you to use isinstance
is upon entry to a function that's called from outside your area of control - for example within the API of a function, method, module or package that you've written for others to use, and you want to check they're passing you sensible parameters. See [here]
for an example. (written 2016-11-03)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articlesY106 - Object Oriented Python 
Why populate object with values as you construct them? - (2016-02-18) 
From single block to structure and object oriented programming - (2015-12-02) 
What is the difference between a function and a method? - (2015-03-04) 
Simple OO demonstration in C++, comparison to Python - (2013-07-01) 
Really Simple Class and Inheritance example in Python - (2013-03-04) 
Spike solution, refactored and reusable, Python - Example - (2013-02-28) 
this or self - what are they, and what is the difference? (Python) - (2012-12-08) 
From Structured to Object Oriented Programming. - (2012-10-02) 
Object oriented or structured - a comparison in Python. Also writing clean regular expressions - (2012-03-26) 
Moving from scripting to Object Orientation in Python - (2011-09-13) 
From fish, loaves and apples to money, plastic cards and BACS (Perl references explained) - (2011-08-20) 
Object Oriented Programming for Structured Programmers - conversion training - (2010-12-14) 
Tips for writing a test program (Ruby / Python / Java) - (2010-01-29) 
When should I use OO techniques? - (2009-05-11) 
Python - a truly dynamic language - (2009-01-30) 
Introduction to Object Oriented Programming - (2008-12-06) 
Screw it or Glue it? Access to Object variables - a warning - (2007-09-12) 
Python class rattling around - (2007-08-16) 
Python - function v method - (2006-10-20) 
Python makes University Challenge - (2006-08-15) 
Class, static and unbound variables - (2005-10-25)
Some other Articles
Writing Python 2 such that Python 3 is easyFrom and Import in Python - where is the module loaded from?Conditional operators in PythonEmbedding more complex code into a named blockWhen to check an object type - Python isinstance exampleCelebrating our diversity rather than discriminating for itNesting decoratorsDefining an object that is a modified standard type in Pythonwith in Python - examples of use, and of defining your own contextProfiling your Python program
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