Null object pattern (was: Python 3.0 - is this true?)

Ben Finney bignose+hates-spam at benfinney.id.au
Wed Nov 12 00:17:05 CET 2008


Terry Reedy <tjreedy at udel.edu> writes:

> We're not going to add the "feature" back that None compares smaller
> than everything. It's a slippery slope that ends with all operations
> involving None returning None -- I've seen a proposal made in all
> earnestness requesting that None+42 == None, None() == None, and so
> on. This Nonesense was wisely rejected

I agree with that decision. However, the behaviour you specify *is*
useful (though I don't think ‘None’ should have that behaviour). It is
the “Null object” design pattern, and may be familiar to many
readers in its SQL implementation as the ‘NULL’ non-value.

In fact, there is a Python Cookbook recipe implementing a ‘Null’
object <URL:http://code.activestate.com/recipes/68205/> that also
features in the O'Reilly _Python Cookbook, second edition_.

-- 
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Ben Finney



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