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authorAndrew M. Kuchling <amk@amk.ca>2006-04-25 12:47:25 (GMT)
committerAndrew M. Kuchling <amk@amk.ca>2006-04-25 12:47:25 (GMT)
commitd798a181abd2b03ba5358d3528e5f4c78be74980 (patch)
tree3140c3b6710c1ffc0c8a0c055ef459e58e5845b7 /Doc/whatsnew
parentb33842ac51f66a7b29642fc672b143b0fbf44788 (diff)
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Rework context terminology
Diffstat (limited to 'Doc/whatsnew')
-rw-r--r--Doc/whatsnew/whatsnew25.tex43
1 files changed, 22 insertions, 21 deletions
diff --git a/Doc/whatsnew/whatsnew25.tex b/Doc/whatsnew/whatsnew25.tex
index 5f60c9e..b062fef 100644
--- a/Doc/whatsnew/whatsnew25.tex
+++ b/Doc/whatsnew/whatsnew25.tex
@@ -667,13 +667,13 @@ A high-level explanation of the context management protocol is:
\begin{itemize}
\item The expression is evaluated and should result in an object
-with a \method{__context__()} method (called a ``context specifier'').
+with a \method{__context__()} method (called a ``context manager'').
\item The context specifier's \method{__context__()} method is called,
-and must return another object (called a ``context manager'') that has
+and must return another object (called a ``with-statement context object'') that has
\method{__enter__()} and \method{__exit__()} methods.
-\item The context manager's \method{__enter__()} method is called. The value
+\item The context object's \method{__enter__()} method is called. The value
returned is assigned to \var{VAR}. If no \code{'as \var{VAR}'} clause
is present, the value is simply discarded.
@@ -685,7 +685,8 @@ with the exception's information, the same values returned by
\function{sys.exc_info()}. The method's return value controls whether
the exception is re-raised: any false value re-raises the exception,
and \code{True} will result in suppressing it. You'll only rarely
-want to suppress the exception; the author of the code containing the
+want to suppress the exception, because if you do
+the author of the code containing the
'\keyword{with}' statement will never realize anything went wrong.
\item If \var{BLOCK} didn't raise an exception,
@@ -724,14 +725,14 @@ First, the \class{DatabaseConnection} needs a \method{__context__()}
method. Sometimes an object can simply return \code{self}; the
\module{threading} module's lock objects do this, for example. For
our database example, though, we need to create a new object; I'll
-call this class \class{DatabaseContextMgr}. Our \method{__context__()}
+call this class \class{DatabaseContext}. Our \method{__context__()}
method must therefore look like this:
\begin{verbatim}
class DatabaseConnection:
...
def __context__ (self):
- return DatabaseContextMgr(self)
+ return DatabaseContext(self)
# Database interface
def cursor (self):
@@ -742,12 +743,12 @@ class DatabaseConnection:
"Rolls back current transaction"
\end{verbatim}
-Instance of \class{DatabaseContextMgr} need the connection object so that
+Instances of \class{DatabaseContext} need the connection object so that
the connection object's \method{commit()} or \method{rollback()}
methods can be called:
\begin{verbatim}
-class DatabaseContextMgr:
+class DatabaseContext:
def __init__ (self, connection):
self.connection = connection
\end{verbatim}
@@ -759,7 +760,7 @@ then add \code{as cursor} to their '\keyword{with}' statement to bind
the cursor to a variable name.
\begin{verbatim}
-class DatabaseContextMgr:
+class DatabaseContext:
...
def __enter__ (self):
# Code to start a new transaction
@@ -779,7 +780,7 @@ wished, you could be more explicit and add a \keyword{return}
statement at the marked location.
\begin{verbatim}
-class DatabaseContextMgr:
+class DatabaseContext:
...
def __exit__ (self, type, value, tb):
if tb is None:
@@ -798,8 +799,8 @@ The new \module{contextlib} module provides some functions and a
decorator that are useful for writing objects for use with the
'\keyword{with}' statement.
-The decorator is called \function{contextmanager}, and lets you write
-a simple context manager as a generator function. The generator
+The decorator is called \function{contextfactory}, and lets you write
+a single generator function instead of defining a new class. The generator
should yield exactly one value. The code up to the \keyword{yield}
will be executed as the \method{__enter__()} method, and the value
yielded will be the method's return value that will get bound to the
@@ -812,9 +813,9 @@ Our database example from the previous section could be written
using this decorator as:
\begin{verbatim}
-from contextlib import contextmanager
+from contextlib import contextfactory
-@contextmanager
+@contextfactory
def db_transaction (connection):
cursor = connection.cursor()
try:
@@ -831,13 +832,12 @@ with db_transaction(db) as cursor:
\end{verbatim}
You can also use this decorator to write the \method{__context__()}
-method for a class without having to create a new class representing
-the context manager:
+method for a class:
\begin{verbatim}
class DatabaseConnection:
- @contextmanager
+ @contextfactory
def __context__ (self):
cursor = self.cursor()
try:
@@ -850,10 +850,11 @@ class DatabaseConnection:
\end{verbatim}
-There's a \function{nested(\var{mgr1}, \var{mgr2}, ...)} function that
-combines a number of contexts so you don't need to write
-nested '\keyword{with}' statements. This example statement does two
-things, starting a database transaction and acquiring a thread lock:
+The \module{contextlib} module also has a \function{nested(\var{mgr1},
+\var{mgr2}, ...)} function that combines a number of contexts so you
+don't need to write nested '\keyword{with}' statements. In this
+example, the single '\keyword{with}' statement both starts a database
+transaction and acquires a thread lock:
\begin{verbatim}
lock = threading.Lock()