Re: Scoping and locating definitions

On Jan 20, 2007, at 3:31 PM, Jos Backus wrote:

> On Sun, Jan 21, 2007 at 08:19:47AM +0900, Pit Capitain wrote:
>> Jos, just out of curiosity, could you show us (or me via private  
>> mail,
>> if you think it's too offtopic for ruby-core) how you would do  
>> what you
>> want in Python?
>
> Pit, I'm really sorry but I'm not well-versed enough in Python to  
> be able to
> demonstrate this. I've cc'd my colleague and will ask him for an  
> example.

I'm that colleague.  I'm not the world's best Python expert either,  
but I think the answer is that "you don't".

That is, you don't extend the String class to add a rot13 method,  
because Python doesn't have open classes like that.  (I think it can  
possibly be done, but only awkwardly; the language does not encourage  
it.)

If you want to provide rot13 functionaliy, you'll put it in a  
function in a package that does it.  Anyone who wants to rot13 will  
explicitly import your package.

The point is, in Python, if file A chooses to import package B, it is  
very unlikely to affect code operating in completely unrelated file  
C.  In Ruby, it's entirely possible that the import of B could have  
broken something that C depended on.

If you are in a world where all the code is written by good,  
competent programmers who've agreed on the ground rules, Ruby can  
give them all a lot of power.  But if you're not so sure about your  
fellow programmers, or about code that you are loading off the net,  
then Ruby's model offers much less protection than Python's.

This kind of thing would make me much more scared to work on a big  
project in Ruby than I would be in Python.  (I haven't yet had the  
opportunity to work on a big project in either, so I'm not actually  
talking from experience.)

- Terry