[Python-Dev] None as a keyword (original) (raw)

[Python-Dev] None as a keyword / class methods

Donald Beaudry Donald Beaudry donb@init.com
Tue, 28 Mar 2000 15:46:06 -0500

...sorry to jump in on the middle of this one, but.

A while back I put a lot of thought into how to support class methods and class attributes. I feel that I solved the problem in a fairly complete way though the solution does have some warts. Here's an example:

class foo(base): ... value = 10 # this is an instance attribute called 'value' ... # as usual, it is shared between all instances ... # until explicitly set on a particular instance ... ... def set_value(self, x): ... print "instance method" ... self.value = x ... ... # ... # here come the weird part ... # ... class class: ... value = 5 # this is a class attribute called value ... ... def set_value(cl, x): ... print "class method" ... cl.value = x ... ... def set_instance_default_value(cl, x): ... cl._.value = x ... f = foo() f.value 10 foo.value = 20 f.value 10 f.class.value 20 foo..value 10 foo..value = 1 f.value 1 foo.setvalue(100) class method foo.value 100 f.value 1 f.setvalue(40) instance method f.value 40 foo..value 1 ff=foo() foo.setinstancedefaultvalue(15) ff.value 15 foo..setvalue(ff, 5) instance method ff.value 5

Is anyone still with me?

The crux of the problem is that in the current python class/instance implementation, classes dont have attributes of their own. All of those things that look like class attributes are really there as defaults for the instances. To support true class attributes a new name space must be invented. Since I wanted class objects to look like any other object, I chose to move the "instance defaults" name space under the underscore attribute. This allows the class's unqualified namespace to refer to its own attributes. Clear as mud, right?

In case you are wondering, yes, the code above is a working example. I released it a while back as the 'objectmodule' and just updated it to work with Python-1.5.2. The update has yet to be released.

-- Donald Beaudry Ab Initio Software Corp. 201 Spring Street donb@init.com Lexington, MA 02421 ...Will hack for sushi...