[Python-ideas] why not try without except?

[spir]

Le Sun, 26 Apr 2009 19:05:01 +1000,
Steven D'Aprano <steve at pearwood.info> s'exprima ainsi:

> On Sun, 26 Apr 2009 06:51:08 pm spir wrote:
> 
> > Now I realise that what I miss is a kind of handy, clear, and not
> > misuseable idiom for coping with undefined
> > variables/attributes/parameters. 
> 
> The best way to deal with undefined variables is to make sure that there 
> never are any. In other words: an undefined variable is a bug. Fix the 
> bug, don't hide it.
 
I understand your position, indeed.
Mine is: optional things and optional actions are basic and common notions. Even more in modelizing / programming fields. Are they important enough (for you) to require a dedicated idiom in a (your favorite) PL?

class Shape(object):
   def __init__(self, ..., ?fill_color)
      .......
      ?self.fill_color = fill_color
   def show(self):
      .......
      ?self.fill(self.fill_color)

Moreover, imagine NoReturnValueError instead of None; raised by python when a func call is used as an expression.
   x = f()	# may raise NoReturnValueError
		# will never bind None except explicitely returned
This would first avoid numerous bugs, often difficult to catch because silent:
   y = x.sort()	# awa!
(*) (**)

Also one could then write, for instance:

   def show(self):
      .......
      ?self.fill(self.fill_color)
      ?self.showTansforms(user.getTransforms())

(if NoReturnValueError belongs to the set of error types caught by optional actions)

OK, won't fight for this anyway ;-)


denis


(*) I would also love a way to prevent the opposite bug:
   s.strip()   # awa!
(**) Actually, I must be a fan of Pascal's procedure vs function distinction. Find it sensible and meaningful.

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