Private attribute

Steven D'Aprano steve at
Tue Aug 26 01:55:04 CEST 2008

On Mon, 25 Aug 2008 19:47:38 +0100, Ken Starks wrote:

> I have a class with an attribute called 'gridsize' and I want a derived
> class to force and keep it at 0.8 (representing 8mm).
> Is this a correct, or the most pythonic approach?

Others have already suggested using a property, but I'll suggest that the 
most Pythonic approach is not to be so dogmatic about trying to force it 
to stay at 0.8. Maybe *you* will never want it to change, but can you be 
sure that those calling your class will never want a 9mm grid?

I'd suggest marking it private by convention:

def SomeClass(object):
    _gridsize = 0.8

The leading underscore tells callers that they change the attribute at 
their own risk.

An even more Pythonic approach is to write your class that makes no 
assumptions about gridsize, and thus explicitly supports any reasonable 
grid size. 


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