Variables vs attributes

Miles Kaufmann milesck at umich.edu
Sat Sep 12 09:39:17 CEST 2009


On Apr 17, 2009, at 8:56 PM, Steven D'Aprano wrote:
> If an integer variable is an integer, and a string variable is a  
> string,
> and float variable is a float, and a list variable is a list  
> (there's a
> pattern here), shouldn't a class variable be a class and an instance
> variable be an instance?
>
> I had never noticed the usage of "variable" to mean attribute until  
> a few
> months ago. What's going on? Why did people decide that confusing
> variables and attributes of variables was a good thing? What's next,
> describing dictionary keys as "dictionary variables"?

(Replying to this old message because I've seen you make this point in  
several threads recently)

Let me prefix this by saying: I don't like to use the word "variable"  
when being specific about Python, because its meaning isn't well  
established like "name" or "object".  Personally, I think most people  
use "variable" when they're thinking about Python in terms of C-style  
assignment semantics (which isn't accurate, but as a newbie you can  
get away with it for a little while), or when they're conflating a  
name with the object it refers to.  But I don't think there's a well- 
established definition in Python (because it implies a storage model  
that Python doesn't use), and it certainly isn't synonymous with  
"object".

As far as "class variable" and "instance variable" go:

They're used across many object-oriented languages:
http://en.wikipedia.org/wiki/Class_variable

The Python language reference uses that terminology:
http://docs.python.org/reference/datamodel.html

As does Guido himself:
http://people.csail.mit.edu/rudolph/Teaching/Lectures/guido-intro-2.pdf

We're blessed with a variety of object-oriented almost-synonyms to  
choose from, some of which are more Pythonic than others.  But I don't  
think it's worth "correcting" everyone who uses the phrase "class  
variable", especially when their use of it causes no confusion.

-Miles




More information about the Python-list mailing list