Commits

Nick Coghlan  committed af44db2

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.

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  • Parent commits 14cb2ee
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Files changed (7)

File Doc/lib/libcontextlib.tex

 
 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
 </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
 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
 \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:
 
 \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.
 
 \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
 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}

File Doc/lib/libstdtypes.tex

 \subsection{Context Types \label{typecontext}}
 
 \versionadded{2.5}
-\index{context specification protocol}
+\index{with statement context protocol}
 \index{context management protocol}
-\index{protocol!context specification}
+\index{protocol!with statement context}
 \index{protocol!context management}
 
 Python's \keyword{with} statement supports the concept of a runtime
-context defined by a context specifier.  This is implemented using
+context defined by a context manager.  This is implemented using
 three distinct methods; these are used to allow user-defined
-classes to define a context.
+classes to define a runtime context.
 
-The \dfn{context specification protocol} consists of a single
-method that needs to be provided for a context specifier object to
+The \dfn{context management protocol} consists of a single
+method that needs to be provided for a context manager object to
 define a runtime context:
 
-\begin{methoddesc}[context specifier]{__context__}{}
-  Return a context manager object.  The object is required to support
-  the context management protocol described below.  If an object
-  supports different kinds of runtime context, additional methods can
-  be provided to specifically request context managers for those
-  kinds of context.  (An example of an object supporting multiple kinds
-  of context would be a synchronisation object which supported both
-  a locked context for normal thread synchronisation and an unlocked
-  context to temporarily release a held lock while performing a
-  potentially long running operation)
+\begin{methoddesc}[context manager]{__context__}{}
+  Return a with statement context object.  The object is required to
+  support the with statement context protocol described below.  If an
+  object supports different kinds of runtime context, additional
+  methods can be provided to specifically request context objects for
+  those kinds of runtime context.  (An example of an object supporting
+  multiple kinds of context would be a synchronisation object which
+  supported both a locked context for normal thread synchronisation
+  and an unlocked context to temporarily release a held lock while
+  performing a potentially long running operation)
 \end{methoddesc}
 
-The context manager objects themselves are required to support the
+The with statement context objects themselves are required to support the
 following three methods, which together form the
-\dfn{context management protocol}:
+\dfn{with statement context protocol}:
 
-\begin{methoddesc}[context manager]{__context__}{}
-  Return the context manager object itself.  This is required to
-  allow both context specifiers and context managers to be used with
-  the \keyword{with} statement.
+\begin{methoddesc}[with statement context]{__context__}{}
+  Return the context object itself.  This is required to allow both
+  context objects and context managers to be used in a \keyword{with}
+  statement.
 \end{methoddesc}
 
-\begin{methoddesc}[context manager]{__enter__}{}
+\begin{methoddesc}[with statement context]{__enter__}{}
   Enter the runtime context and return either the defining context
-  specifier or another object related to the runtime context. The value
+  manager or another object related to the runtime context. The value
   returned by this method is bound to the identifier in the
   \keyword{as} clause of \keyword{with} statements using this context.
-  (An example of a context with a context manager that returns the
-  original context specifier is file objects, which are returned from
-  __enter__() to allow \function{open()} to be used directly in a with
-  statement. An example of a context manager that returns a related
+  (An example of a context object that returns the original context
+  manager is file objects, which are returned from __enter__() to
+  allow \function{open()} to be used directly in a with
+  statement. An example of a context object that returns a related
   object is \code{decimal.Context} which sets the active decimal
-  context to a copy of the context specifier and then returns the copy
-  to allow changes to be made to the current decimal context in the
-  body of the \keyword{with} statement) without affecting code outside
+  context to a copy of the context manager and then returns the copy.
+  This allows changes to be made to the current decimal context in the
+  body of the \keyword{with} statement without affecting code outside
   the \keyword{with} statement).
 \end{methoddesc}
 
-\begin{methoddesc}[context manager]{__exit__}{exc_type, exc_val, exc_tb}
+\begin{methoddesc}[with statement context]{__exit__}{exc_type, exc_val, exc_tb}
   Exit the runtime context and return a Boolean flag indicating if any
   expection that occurred should be suppressed. If an exception
   occurred while executing the body of the \keyword{with} statement, the
   \method{__exit__()} method has actually failed.
 \end{methoddesc}
 
-Python defines several context specifiers and managers to support
+Python defines several context objects and managers to support
 easy thread synchronisation, prompt closure of files or other
 objects, and thread-safe manipulation of the decimal arithmetic
 context. The specific types are not important beyond their
-implementation of the context specification and context
-management protocols.
+implementation of the context management and with statement context
+protocols.
 
-Python's generators and the \code{contextlib.contextmanager}
-decorator provide a convenient way to implement the context
-specification and context management protocols.  If a context
-specifier's \method{__context__()} method is implemented as a
-generator decorated with the \code{contextlib.contextmanager}
-decorator, it will automatically return a context manager
+Python's generators and the \code{contextlib.contextfactory} decorator
+provide a convenient way to implement these protocols.  If a context
+manager's \method{__context__()} method is implemented as a
+generator decorated with the \code{contextlib.contextfactory}
+decorator, it will automatically return a with statement context
 object supplying the necessary \method{__context__()},
 \method{__enter__()} and \method{__exit__()} methods.
 

File Doc/ref/ref3.tex

 
 \end{itemize}
 
-\subsection{Context Specifiers and Managers\label{context-managers}}
+\subsection{With Statement Contexts and Context Managers\label{context-managers}}
 
 \versionadded{2.5}
 
-A \dfn{context specifier} is an object that defines the runtime
+A \dfn{context manager} is an object that defines the runtime
 context to be established when executing a \keyword{with}
-statement. The context specifier provides a \dfn{context manager}
-which manages the entry into, and the exit from, the desired
-runtime context for the execution of the block of code.  Context
-managers are normally invoked using the \keyword{with} statement
-(described in section~\ref{with}), but can also be used by
-directly invoking their methods.
+statement. The context manager provides a
+\dfn{with statement context object} which manages the entry into,
+and the exit from, the desired runtime context for the execution
+of the block of code.  Context managers are normally invoked using
+the \keyword{with} statement (described in section~\ref{with}), but
+can also be used by directly invoking their methods.
 
 \stindex{with}
 \index{context manager}
-\index{context specifier}
+\index{context (with statement)}
+\index{with statement context}
 
-Typical uses of context specifiers and managers include saving and
+Typical uses of context managers and contexts include saving and
 restoring various kinds of global state, locking and unlocking
 resources, closing opened files, etc.
 
-For more information on context specifiers and context manager objects,
+For more information on context managers and context objects,
 see ``\ulink{Context Types}{../lib/typecontext.html}'' in the
 \citetitle[../lib/lib.html]{Python Library Reference}.
 
-\begin{methoddesc}[context specifier]{__context__}{self}
+\begin{methoddesc}[context manager]{__context__}{self}
 Invoked when the object is used as the context expression of a
 \keyword{with} statement.  The returned object must implement
 \method{__enter__()} and \method{__exit__()} methods.
 
-Context specifiers written in Python can also implement this method
+Context managers written in Python can also implement this method
 using a generator function decorated with the
-\function{contextlib.contextmanager} decorator, as this can be simpler
+\function{contextlib.contextfactory} decorator, as this can be simpler
 than writing individual \method{__enter__()} and \method{__exit__()}
 methods on a separate object when the state to be managed is complex.
 
-Context manager objects also need to implement this method; they are
-required to return themselves (that is, this method will simply
+With statement context objects also need to implement this method; they
+are required to return themselves (that is, this method will simply
 return \var{self}).
 \end{methoddesc}
 
-\begin{methoddesc}[context manager]{__enter__}{self}
-Enter the context managed by this object. The \keyword{with} statement
-will bind this method's return value to the target(s) specified in the
-\keyword{as} clause of the statement, if any.
+\begin{methoddesc}[with statement context]{__enter__}{self}
+Enter the runtime context related to this object. The \keyword{with}
+statement will bind this method's return value to the target(s)
+specified in the \keyword{as} clause of the statement, if any.
 \end{methoddesc}
 
 \begin{methoddesc}[context manager]{__exit__}
 {self, exc_type, exc_value, traceback}
-Exit the context managed by this object. The parameters describe the
-exception that caused the context to be exited. If the context was
-exited without an exception, all three arguments will be
-\constant{None}.
+Exit the runtime context related to this object. The parameters
+describe the exception that caused the context to be exited. If
+the context was exited without an exception, all three arguments
+will be \constant{None}.
 
 If an exception is supplied, and the method wishes to suppress the
 exception (i.e., prevent it from being propagated), it should return a

File Doc/ref/ref7.tex

 \versionadded{2.5}
 
 The \keyword{with} statement is used to wrap the execution of a block
-with methods defined by a context specifier or manager (see
-section~\ref{context-managers}). This allows common
+with methods defined by a context manager or with statement context
+object (see section~\ref{context-managers}). This allows common
 \keyword{try}...\keyword{except}...\keyword{finally} usage patterns to
-be encapsulated as context specifiers or managers for convenient reuse.
+be encapsulated for convenient reuse.
 
 \begin{productionlist}
   \production{with_stmt}
 
 \begin{enumerate}
 
-\item The expression is evaluated, to obtain a context specifier.
+\item The context expression is evaluated, to obtain a context manager.
 
-\item The context specifier's \method{__context__()} method is
-invoked to obtain a context manager object.
+\item The context manger's \method{__context__()} method is
+invoked to obtain a with statement context object.
 
-\item The context manager's \method{__enter__()} method is invoked.
+\item The context object's \method{__enter__()} method is invoked.
 
 \item If a target list was included in the \keyword{with}
 statement, the return value from \method{__enter__()} is assigned to it.
 
 \item The suite is executed.
 
-\item The context manager's \method{__exit__()} method is invoked. If
+\item The context object's \method{__exit__()} method is invoked. If
 an exception caused the suite to be exited, its type, value, and
 traceback are passed as arguments to \method{__exit__()}. Otherwise,
 three \constant{None} arguments are supplied.

File Lib/contextlib.py

 
 import sys
 
-__all__ = ["contextmanager", "nested", "closing"]
+__all__ = ["contextfactory", "nested", "closing"]
 
-class GeneratorContextManager(object):
-    """Helper for @contextmanager decorator."""
+class GeneratorContext(object):
+    """Helper for @contextfactory decorator."""
 
     def __init__(self, gen):
         self.gen = gen
                     raise
 
 
-def contextmanager(func):
-    """@contextmanager decorator.
+def contextfactory(func):
+    """@contextfactory decorator.
 
     Typical usage:
 
 
     """
     def helper(*args, **kwds):
-        return GeneratorContextManager(func(*args, **kwds))
+        return GeneratorContext(func(*args, **kwds))
     try:
         helper.__name__ = func.__name__
         helper.__doc__ = func.__doc__
     return helper
 
 
-@contextmanager
+@contextfactory
 def nested(*contexts):
     """Support multiple context managers in a single with-statement.
 
             raise exc[0], exc[1], exc[2]
 
 
-@contextmanager
-def closing(thing):
-    """Context manager to automatically close something at the end of a block.
+class closing(object):
+    """Context to automatically close something at the end of a block.
 
     Code like this:
 
             f.close()
 
     """
-    try:
-        yield thing
-    finally:
-        thing.close()
+    def __init__(self, thing):
+        self.thing = thing
+    def __context__(self):
+        return self
+    def __enter__(self):
+        return self.thing
+    def __exit__(self, *exc_info):
+        self.thing.close()

File Lib/decimal.py

 
 del name, val, globalname, rounding_functions
 
-class ContextManager(object):
+class WithStatementContext(object):
     """Helper class to simplify Context management.
 
     Sample usage:
         return ', '.join(s) + ')'
 
     def __context__(self):
-        return ContextManager(self.copy())
+        return WithStatementContext(self.copy())
 
     def clear_flags(self):
         """Reset all flags to zero"""

File Lib/test/test_contextlib.py

 
 class ContextManagerTestCase(unittest.TestCase):
 
-    def test_contextmanager_plain(self):
+    def test_contextfactory_plain(self):
         state = []
-        @contextmanager
+        @contextfactory
         def woohoo():
             state.append(1)
             yield 42
             state.append(x)
         self.assertEqual(state, [1, 42, 999])
 
-    def test_contextmanager_finally(self):
+    def test_contextfactory_finally(self):
         state = []
-        @contextmanager
+        @contextfactory
         def woohoo():
             state.append(1)
             try:
             self.fail("Expected ZeroDivisionError")
         self.assertEqual(state, [1, 42, 999])
 
-    def test_contextmanager_no_reraise(self):
-        @contextmanager
+    def test_contextfactory_no_reraise(self):
+        @contextfactory
         def whee():
             yield
         ctx = whee().__context__()
         # Calling __exit__ should not result in an exception
         self.failIf(ctx.__exit__(TypeError, TypeError("foo"), None))
 
-    def test_contextmanager_trap_yield_after_throw(self):
-        @contextmanager
+    def test_contextfactory_trap_yield_after_throw(self):
+        @contextfactory
         def whoo():
             try:
                 yield
             RuntimeError, ctx.__exit__, TypeError, TypeError("foo"), None
         )
 
-    def test_contextmanager_except(self):
+    def test_contextfactory_except(self):
         state = []
-        @contextmanager
+        @contextfactory
         def woohoo():
             state.append(1)
             try:
             raise ZeroDivisionError(999)
         self.assertEqual(state, [1, 42, 999])
 
-    def test_contextmanager_attribs(self):
+    def test_contextfactory_attribs(self):
         def attribs(**kw):
             def decorate(func):
                 for k,v in kw.items():
                     setattr(func,k,v)
                 return func
             return decorate
-        @contextmanager
+        @contextfactory
         @attribs(foo='bar')
         def baz(spam):
             """Whee!"""
     # XXX This needs more work
 
     def test_nested(self):
-        @contextmanager
+        @contextfactory
         def a():
             yield 1
-        @contextmanager
+        @contextfactory
         def b():
             yield 2
-        @contextmanager
+        @contextfactory
         def c():
             yield 3
         with nested(a(), b(), c()) as (x, y, z):
 
     def test_nested_cleanup(self):
         state = []
-        @contextmanager
+        @contextfactory
         def a():
             state.append(1)
             try:
                 yield 2
             finally:
                 state.append(3)
-        @contextmanager
+        @contextfactory
         def b():
             state.append(4)
             try:
 
     def test_nested_right_exception(self):
         state = []
-        @contextmanager
+        @contextfactory
         def a():
             yield 1
         class b(object):
             self.fail("Didn't raise ZeroDivisionError")
 
     def test_nested_b_swallows(self):
-        @contextmanager
+        @contextfactory
         def a():
             yield
-        @contextmanager
+        @contextfactory
         def b():
             try:
                 yield
             self.fail("Didn't swallow ZeroDivisionError")
 
     def test_nested_break(self):
-        @contextmanager
+        @contextfactory
         def a():
             yield
         state = 0
         self.assertEqual(state, 1)
 
     def test_nested_continue(self):
-        @contextmanager
+        @contextfactory
         def a():
             yield
         state = 0
         self.assertEqual(state, 3)
 
     def test_nested_return(self):
-        @contextmanager
+        @contextfactory
         def a():
             try:
                 yield