Declaring a class level nested class?

[Jean-Michel Pichavant]

Chris Rebert wrote:
> On Wed, Dec 2, 2009 at 8:55 PM, cmckenzie <mckenzie.c at gmail.com> wrote:
>   
>> Hi.
>>
>> I'm new to Python, but I've managed to make some nice progress up to
>> this point. After some code refactoring, I ran into a class design
>> problem and I was wondering what the experts thought. It goes
>> something like this:
>>
>> class module:
>>   nestedClass
>>
>>   def __init__():
>>      self.nestedClass = nested()
>>      print self.nestedClass.nestedVar
>>
>>   class nested():
>>      nestedVar = 1
>>      def __init__(self):
>>         print "Initialized..."
>>
>> I can't figure out what the correct way to construct the "nested"
>> class so it can belong to "module".
>>
>> I want a class level construct of "nested" to belong to "module", but
>> I keep getting nestedClass isn't defined.
>>     
>
> Here's the scoping reason why it fails (remember that the nested class
> is a class variable of the containing class):
>
> [snip interesting reminder/faq]
>
> However, there's pretty much no reason to nest classes anyway in
> Python (it's not Java!). 
A little bit off topic,ahere is a nested class pattern I'm using quite 
often :

class Device
    """Holds the different device services."""

    class OS: # UPPERCASE  means it holds constants
        """Operating system of one device."""
        VXWORKS = 'vxWorks'
        ECOS = 'ecos'
   
    def init(self, _os = None):
       self.os = _os

device = Device(Device.OS.VXWORKS)

Whenever I get a Device instance in my code I can match its OS without 
tedious imports:

# no "from whatever import Device" is required
if device.os is device.OS.VXWORKS:
    print 'you are using vxWorks'


I'm using this pattern whenever I can now:
1/ it removes all magically 'inside code' defined strings or numbers, 
only class attributes are used.
2/ if required, it allows to write complete and detailed documentation 
for nested class constants
3/ you can match attributes with the nested class values without further 
import, everything is accessible from the instance itself

JM