internal circular class references

[James Stroud]

Ethan Furman wrote:
> Greetings List!
> 
> I'm writing a wrapper to the datetime.date module to support having no 
> date.  Its intended use is to hold a date value from a dbf file, which 
> can be empty.
> 
> The class is functional at this point, but there is one thing I would 
> like to change -- datetime.date.max and datetime.date.min are class 
> attributes of datetime.date, and hold datetime.date values.  At this 
> point I have to have two lines outside the actual class definition to do 
> the same thing, e.g.:
> 
> <trimmed down class code>
>   class NullDate(object):
>       "adds null capable DateTime.Date constructs"
>       __slots__ = ['_date']
>       def __new__(cls, date='', month=0, day=0):
>           nulldate = object.__new__(cls)
>           nulldate._date = ""
>           .
>         .
>         .
>         return nulldate
>       def __getattr__(self, name):
>           if self:
>               attribute = self._date.__getattribute__(name)
>               return attribute
>           else:
>               if callable(dt.date.__dict__[name]):
>                   return int
>               else:
>                   return 0
>       def __nonzero__(self):
>           if self._date:
>               return True
>           return False
>       @classmethod
>       def fromordinal(cls, number):
>           if number:
>               return cls(dt.date.fromordinal(number))
>           else:
>               return cls()
>   NullDate.max = NullDate(dt.date.max)
>   NullDate.min = NullDate(dt.date.min)
> </trimmed down class code>
> 
> How can I move those last two lines into the class definition so that:
>   1) they are class attributes (not instance), and
>   2) they are NullDate type objects?
> 
> ~ethan~

I resisted posting a similar question recently. After much 
consideration, I realized that the inability to reference a class inside 
its own definition must have been a deliberate design of the language. 
So the short answer is you can't.

The way you have done it is best--its not a hack and is good style.

James