[Py-howto-checkins] CVS: pyhowto python-21.tex,1.17,1.18

[A.M. K. <aku...@us...>]

Update of /cvsroot/py-howto/pyhowto
In directory usw-pr-cvs1:/tmp/cvs-serv26887

Modified Files:
	python-21.tex 
Log Message:
Discuss PEP 236.
Update nested scope section.


Index: python-21.tex
===================================================================
RCS file: /cvsroot/py-howto/pyhowto/python-21.tex,v
retrieving revision 1.17
retrieving revision 1.18
diff -C2 -r1.17 -r1.18
*** python-21.tex	2001/03/02 21:19:38	1.17
--- python-21.tex	2001/03/03 03:25:04	1.18
***************
*** 91,95 ****
  variable within a function that contains further function definitions.
  This seems rather unlikely though, since such code would have been
! pretty confusing to read in the first place.
  
  One side effect of the change is that the \code{from \var{module}
--- 91,95 ----
  variable within a function that contains further function definitions.
  This seems rather unlikely though, since such code would have been
! pretty confusing to read in the first place.  
  
  One side effect of the change is that the \code{from \var{module}
***************
*** 127,130 ****
--- 127,138 ----
  poor design anyway).
  
+ Compatibility concerns have led to nested scopes being introduced
+ gradually; in Python 2.1, they aren't enabled by default, but can be
+ turned on within a module by using a future statement as described in
+ PEP 236.  (See the following section for further discussion of PEP
+ 236.)  In Python 2.2, nested scopes will become the default and there
+ will be no way to turn them off, but users will have had all of 2.1's
+ lifetime to fix any breakage resulting from their introduction.
+ 
  \begin{seealso}
  
***************
*** 137,142 ****
  %======================================================================
  \section{PEP 236: \module{__future__} Directives}
  
! XXX
  
  %======================================================================
--- 145,177 ----
  %======================================================================
  \section{PEP 236: \module{__future__} Directives}
+ 
+ The reaction to nested scopes was widespread concern about the dangers
+ of breaking code with the 2.1 release, and it was strong enough to
+ make the Pythoneers take a more conservative approach.  This approach
+ consists of introducing a convention for enabling optional
+ functionality in release N that will become compulsory in release N+1.  
+ 
+ The syntax uses a \code{from...import} statement using the reserved
+ module name \module{__future__}.  Nested scopes can be enabled by the
+ following statement:
+ 
+ \begin{verbatim}
+ from __future__ import nested_scopes
+ \end{verbatim}
  
! While it looks like a normal \keyword{import} statement, it's not;
! there are strict rules on where such a future statement can be put.
! They can only be at the top of a module, and must precede any Python
! code or regular \keyword{import} statements.  This is because such
! statements can affect how the Python bytecode compiler parses code and
! generates bytecode, so they must precede any statement that will
! result in bytecodes being produced.
! 
! \begin{seealso}
! 
! \seepep{236}{Back to the \module{__future__}}{Written by Tim Peters,
! and primarily implemented by Jeremy Hylton.}
! 
! \end{seealso}
  
  %======================================================================