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
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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
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*** 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}
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*** 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}
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*** 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}
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