[Python-checkins] python/nondist/peps pep-0343.txt,1.14,1.15

[gvanrossum@users.sourceforge.net]

Update of /cvsroot/python/python/nondist/peps
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv407

Modified Files:
	pep-0343.txt 
Log Message:
More generic decimal example.


Index: pep-0343.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0343.txt,v
retrieving revision 1.14
retrieving revision 1.15
diff -u -d -r1.14 -r1.15
--- pep-0343.txt	18 May 2005 03:58:29 -0000	1.14
+++ pep-0343.txt	18 May 2005 14:24:27 -0000	1.15
@@ -418,19 +418,28 @@
             # so this must be outside the do-statement:
             return +s
 
-       An alternative version of the generator saves the entire
-       context instead of just the precision attribute.  This is more
-       robust, but also more expensive, making it perhaps the better
-       choice when several attributes are modified together:
+    9. Here's a more general Decimal-context-switching template:
 
         @do_template
-        def with_extra_precision(places=2):
-            oldcontext = decimal.getcontext()
-            newcontext = oldcontext.copy()
-            newcontext.prec += places
-            decimal.setcontext(newcontext)
-            yield None
-            decimal.setcontext(oldcontext)
+        def with_decimal_context(newctx=None):
+            oldctx = decimal.getcontext()
+            if newctx is None:
+                newctx = oldctx.copy()
+            decimal.setcontext(newctx)
+            yield newctx
+            decimal.setcontext(oldctx)
+
+       Sample usage (adapted from the previous one):
+
+        def sin(x):
+            do with_decimal_context() as ctx:
+                ctx.prec += 2
+                # Rest of algorithm the same
+            return +s
+
+       (Nick Coghlan has proposed to add __enter__ and __exit__
+       methods to the decimal.Context class so that this example can
+       be simplified to "do decimal.getcontext() as ctx: ...".)
 
 References