Move the PEP 343 documentation and implementation closer to the

terminology in the alpha 1 documentation.

 - "context manager" reverts to its alpha 1 definition
 - the term "context specifier" goes away entirely
 - contextlib.GeneratorContextManager is renamed GeneratorContext

There are still a number of changes relative to alpha 1:

  - the expression in the with statement is explicitly called the
    "context expression" in the language reference
  - the terms 'with statement context', 'context object' or 'with
    statement context' are used in several places instead of a bare
    'context'. The aim of this is to avoid ambiguity in relation to the
    runtime context set up when the block is executed, and the context
    objects that already exist in various application domains (such as
    decimal.Context)
  - contextlib.contextmanager is renamed to contextfactory
    This best reflects the nature of the function resulting from the
    use of that decorator
  - decimal.ContextManager is renamed to WithStatementContext
    Simple dropping the 'Manager' part wasn't possible due to the
    fact that decimal.Context already exists and means something
    different. WithStatementContext is ugly but workable.

A technically unrelated change snuck into this commit:
contextlib.closing now avoids the overhead of creating a
generator, since it's trivial to implement that particular
context manager directly.

1 files changed, 47 insertions, 26 deletions

diff --git a/Doc/lib/libcontextlib.tex b/Doc/lib/libcontextlib.tex
index 2a9eb0e..f212174 100644
--- a/Doc/lib/libcontextlib.tex
+++ b/Doc/lib/libcontextlib.tex
@@ -11,18 +11,19 @@ This module provides utilities for common tasks involving the
 
 Functions provided:
 
-\begin{funcdesc}{contextmanager}{func}
-This function is a decorator that can be used to define context managers
-for use with the \keyword{with} statement, without needing to create a
-class or separate \method{__enter__()} and \method{__exit__()} methods.
+\begin{funcdesc}{context}func}
+This function is a decorator that can be used to define a factory
+function for \keyword{with} statement context objects, without
+needing to create a class or separate \method{__enter__()} and
+\method{__exit__()} methods.
 
 A simple example:
 
 \begin{verbatim}
 from __future__ import with_statement
-from contextlib import contextmanager
+from contextlib import contextfactory
 
-@contextmanager
+@contextfactory
 def tag(name):
     print "<%s>" % name
     yield
@@ -36,9 +37,10 @@ foo
 </h1>
 \end{verbatim}
 
-When called, the decorated function must return a generator-iterator.
-This iterator must yield exactly one value, which will be bound to the
-targets in the \keyword{with} statement's \keyword{as} clause, if any.
+The function being decorated must return a generator-iterator when
+called. This iterator must yield exactly one value, which will be
+bound to the targets in the \keyword{with} statement's \keyword{as}
+clause, if any.
 
 At the point where the generator yields, the block nested in the
 \keyword{with} statement is executed.  The generator is then resumed
@@ -53,20 +55,20 @@ reraise that exception. Otherwise the \keyword{with} statement will
 treat the exception as having been handled, and resume execution with
 the statement immediately following the \keyword{with} statement.
 
-Note that you can use \code{@contextmanager} to define a context
-specifier's \method{__context__} method.  This is usually more
+Note that you can use \code{@contextfactory} to define a context
+manager's \method{__context__} method.  This is usually more
 convenient than creating another class just to serve as a context
-manager. For example:
+object. For example:
 
 \begin{verbatim}
 from __future__ import with_statement
-from contextlib import contextmanager
+from contextlib import contextfactory
 
 class Tag:
     def __init__(self, name):
         self.name = name
         
-    @contextmanager
+    @contextfactory
     def __context__(self):
         print "<%s>" % self.name
         yield self
@@ -83,7 +85,7 @@ hello from <__main__.Tag instance at 0x402ce8ec>
 \end{funcdesc}
 
 \begin{funcdesc}{nested}{ctx1\optional{, ctx2\optional{, ...}}}
-Combine multiple context specifiers into a single nested context manager.
+Combine multiple context managers into a single nested context manager.
 
 Code like this:
 
@@ -104,12 +106,12 @@ with A as X:
 \end{verbatim}
 
 Note that if the \method{__exit__()} method of one of the nested
-context managers indicates an exception should be suppressed, no
+context objects indicates an exception should be suppressed, no
 exception information will be passed to any remaining outer context
-managers. Similarly, if the \method{__exit__()} method of one of the
-nested context managers raises an exception, any previous exception
+objects. Similarly, if the \method{__exit__()} method of one of the
+nested context objects raises an exception, any previous exception
 state will be lost; the new exception will be passed to the
-\method{__exit__()} methods of any remaining outer context managers.
+\method{__exit__()} methods of any remaining outer context objects.
 In general, \method{__exit__()} methods should avoid raising
 exceptions, and in particular they should not re-raise a
 passed-in exception.
@@ -117,13 +119,13 @@ passed-in exception.
 
 \label{context-closing}
 \begin{funcdesc}{closing}{thing}
-Return a context manager that closes \var{thing} upon completion of the
+Return a context that closes \var{thing} upon completion of the
 block.  This is basically equivalent to:
 
 \begin{verbatim}
-from contextlib import contextmanager
+from contextlib import contextfactory
 
-@contextmanager
+@contextfactory
 def closing(thing):
     try:
         yield thing
@@ -137,14 +139,33 @@ from __future__ import with_statement
 from contextlib import closing
 import codecs
 
-with closing(urllib.urlopen('http://www.python.org')) as f:
-    for line in f:
+with closing(urllib.urlopen('http://www.python.org')) as page:
+    for line in page:
         print line
 \end{verbatim}
 
-without needing to explicitly close \code{f}.  Even if an error occurs,
-\code{f.close()} will be called when the \keyword{with} block is exited.
+without needing to explicitly close \code{page}.  Even if an error
+occurs, \code{page.close()} will be called when the \keyword{with}
+block is exited.
 
+Context managers with a close method can use this context factory
+directly without needing to implement their own
+\method{__context__()} method.
+\begin{verbatim}
+from __future__ import with_statement
+from contextlib import closing
+
+class MyClass:
+    def close(self):
+        print "Closing", self
+    __context__ = closing
+
+>>> with MyClass() as x:
+...     print "Hello from", x
+...
+Hello from <__main__.MyClass instance at 0xb7df02ec>
+Closing <__main__.MyClass instance at 0xb7df02ec>
+\end{verbatim}
 \end{funcdesc}
 
 \begin{seealso}