[Python-checkins] python/nondist/peps pep-0343.txt,1.2,1.3

Sat May 14 06:02:14 CEST 2005

Update of /cvsroot/python/python/nondist/peps
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv9821
Modified Files:
	pep-0343.txt 
Log Message:
Various clarifications. Mention Decimal context example. Clarify
that I don't like having files etc. implement __enter__ and __exit__
directly.
Index: pep-0343.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0343.txt,v
retrieving revision 1.2
retrieving revision 1.3
diff -u -d -r1.2 -r1.3

--- pep-0343.txt	14 May 2005 02:02:40 -0000	1.2
+++ pep-0343.txt	14 May 2005 04:02:10 -0000	1.3
@@ -57,6 +57,10 @@
 finally:
 abc.__exit__(exc)
 
+ Here, the variables 'abc' and 'exc' are internal variables and not
+ accessible to the user; they will most likely be implemented as
+ special registers or stack positions.
+
 If the "as VAR" part of the syntax is omitted, the "VAR =" part of
 the translation is omitted (but abc.__enter__() is still called).
 
@@ -114,6 +118,32 @@
 A robust implementation of such a decorator should be made part of
 the standard library.
 
+Other Optional Extensions
+
+ It would be possible to endow certain objects, like files,
+ sockets, and locks, with __enter__ and __exit__ methods so that
+ instead of writing
+
+ do locking(myLock):
+ BLOCK
+
+ one could write simply
+
+ do myLock:
+ BLOCK
+
+ I think we should be careful with this; it could lead to mistakes
+ like
+
+ f = open(filename)
+ do f:
+ BLOCK1
+ do f:
+ BLOCK2
+
+ which does not do what one might think (f is closed when BLOCK2 is
+ entered).
+
 Examples
 
 Several of these examples contain "yield None". If PEP 342 is
@@ -194,6 +224,10 @@
 do redirecting_stdout(f):
 print "Hello world"
 
+ This isn't thread-safe, of course, but neither is doing this
+ same dance manually. In a single-threaded program (e.g., a
+ script) it is a totally fine way of doing things.
+
 6. A variant on opening() that also returns an error condition:
 
 @do_template
@@ -226,6 +260,10 @@
 by default all signals are blocked. The implementation is left
 as an exercise to the reader.
 
+ 8. Another use for this feature is the Decimal context. It's left
+ as an exercise for the reader. (Mail it to me if you'd like to
+ see it here.)
+
 Copyright
 
 This document has been placed in the public domain.
