[Python-Dev] Nested functions and class scope

[Guido van Rossum]

John Max Skaller wrote:
> Guido van Rossum wrote:
> ===============>>>>
> > Other issues that need sorting out:
> > 
> > x = 2
> > class C:
> >   x = 1
> >   C = 'some string'
> >   def a(self):
> >      print x
> >   def b(self):
> >      global x
> >      x = 3
> > 
> > class D(C):
> >   C = 'some string'
> >   def a(self):
> >      C.a(self)
> >      print C
> > 
> > o = C()
> > o.a()
> > o.b()
> > o.a()
> > 
> > o = D()
> > o.a()
> > 
> > What would the output look like under your proposal ?
> 
> This is a good point!  If we considered the class as a nested scope
> here, I think it might break too much code, plus it would allow a new
> coding style where you could reference class variables without a self
> or <classname> prefix.  I don't like that prospect, so I'm in favor
> for ruling this out.
> <<<===================
> 
> You're missing the point. you can refer to class variables without
> a prefix right now:
> 
> class X:
> 	x = 1
> 	y = x
> 
> 
> It would be madness NOT to support lexically scoped nested classes
> as well as functions. But note that these scopes only exist
> when a class is executed, that is, when the class is defined.
> This has NO impact on finding class variables from an instance.
> 
> output of above from Vyper:
> --------------------------------------------------------------
> Viperi 2.0.1
> Copyright Maxtal P/L, John Skaller, Australia, 1999
> >>>x = 2
> ...class C:
> ...  x = 1
> ...  C = 'some string'
> ...  def a(self):
> ...     print x
> ...  def b(self):
> ...     global x
> ...     x = 3
> ...
> >>>class D(C):
> ...  C = 'some string'
> ...  def a(self):
> ...     C.a(self)
> ...     print C
> ...
> >>>o = C()
> ...o.a()
> ...o.b()
> ...o.a()
> ...
> 1 
> 3 
> >>>o = D()
> ...o.a()
> ...
> Error Near line 4
> 
> Uncaught Python Exception at top level!!
>   .. Kind: Instance of AttributeError
>   .. Attributes:
>       args --> Cannot find attribute of "some string" "a"
> 
> Traceback (innermost first)
> File: <string> Line: 4
> <cannot get line from file>
> File: <string> Line: 2
> <cannot get line from file>
> 
> -- 
> John (Max) Skaller, mailto:skaller@maxtal.com.au
> 10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
> checkout Vyper http://Vyper.sourceforge.net
> download Interscript http://Interscript.sourceforge.net

Looks like you are missing the point.  Of course I want to keep the
class as a local scope *inside the class def*.  But I need it out of
the way when executing methods.  The example code should print

2			# a() references global x, not C.x
3			# global x got set to three by b()
2			# C refers to global class C
<class C ...>		# ditto

I agree that this is surprising.  But I believe it would break too
much code if we implemented your (simpler) scheme.

--Guido van Rossum (home page: http://www.python.org/~guido/)