[Python-Dev] __slots__ and default values

[Duncan Booth]

Aahz <aahz@pythoncraft.com> wrote in news:20030513141719.GA12321@panix.com:

> On Tue, May 13, 2003, Raymond Hettinger wrote:
>>
>> Was there a reason that __slots__ makes initialized variables
>> read-only?  It would be useful to have overridable default values
>> (even if it entailed copying them into an instance's slots):
>>
>> class Pane(object):
>>     __slots__ = ('background', 'foreground', 'size', 'content')
>>     background = 'black'
>>     foreground = 'white'
>>     size = (80, 25)
>> 
>> p = Pane()
>> p.background = 'light blue'     # override the default
>> assert p.foreground == 'white' # other defaults still in-place
> 
> Why not do the initializing in __init__?

The following works, but I can't remember whether you're supposed to be 
able to use a dict in __slots__ or if it just happens to be allowed:

>>> class Pane(object):
	__slots__ = { 'background': 'black', 'foreground': 'white',
		      'size': (80, 25) }
	def __init__(self):
		for k, v in self.__slots__.iteritems():
			setattr(self, k, v)

			
>>> p = Pane()
>>> p.background = 'blue'
>>> p.background, p.foreground
('blue', 'white')
>>> 

-- 
Duncan Booth                                             duncan@rcp.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?