Method default argument whose type is the class not yet defined

[Roy Smith]

In article <mailman.3570.1352682390.27098.python-list at python.org>,
 Mark Lawrence <breamoreboy at yahoo.co.uk> wrote:

> On 12/11/2012 00:31, Oscar Benjamin wrote:
> >
> > Plain wrong. Vectors are not defined *from any origin*.
> >
> 
> So when the Captain says "full speed ahead, steer 245 degrees", you 
> haven't the faintest idea where you're going, because you have no origin?

Vectors have a length ("full speed ahead") and a direction ("245 
degrees").  What they don't have is a fixed location in space.  The 
captain didn't say, "Full speed ahead, steer 245 degrees, from 45.0N, 
20.0W".

In other words, you are correct.  The order, "full speed ahead, steer 
245 degrees", doesn't give you the faintest idea of where you're going.  
If you were the helmsman, after you executed that order, without any 
additional information (such as your current location), you would have 
no idea what piece of land you will hit, or when you will hit it, if you 
maintain your current course and speed.