[Python-3000] set literals

[Ron Adam]

Raymond Hettinger wrote:

> I'm curious as to whether people will find one-type-with-two-purposes 
> easier to learn that what we have now.  My experience so far is that 
> sets have a near zero learning curve as they are currently implemented.  


And it's not just about ease of learning to use, but also about ease of 
understanding expressed code once it's written.

Having sets as a separate data type makes reading code easier because I 
don't have to first determine the context to determine how it's being used.

Ron