Allow multiple context managers in one with statement, as proposed

in http://codereview.appspot.com/53094 and accepted by Guido.

The construct is transformed into multiple With AST nodes so that
there should be no problems with the semantics.

1 files changed, 18 insertions, 2 deletions

diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst
index afb7ebc..354ed1f 100644
--- a/Doc/reference/compound_stmts.rst
+++ b/Doc/reference/compound_stmts.rst
@@ -333,9 +333,10 @@ allows common :keyword:`try`...\ :keyword:`except`...\ :keyword:`finally` usage
 patterns to be encapsulated for convenient reuse.
 
 .. productionlist::
-   with_stmt: "with" `expression` ["as" `target`] ":" `suite`
+   with_stmt: "with" with_item ("," with_item)* ":" `suite`
+   with_item: `expression` ["as" `target`]
 
-The execution of the :keyword:`with` statement proceeds as follows:
+The execution of the :keyword:`with` statement with one "item" proceeds as follows:
 
 #. The context expression is evaluated to obtain a context manager.
 
@@ -369,12 +370,27 @@ The execution of the :keyword:`with` statement proceeds as follows:
    from :meth:`__exit__` is ignored, and execution proceeds at the normal location
    for the kind of exit that was taken.
 
+With more than one item, the context managers are processed as if multiple
+:keyword:`with` statements were nested::
+
+   with A() as a, B() as b:
+       suite
+
+is equivalent to ::
+
+   with A() as a:
+       with B() as b:
+           suite
+
 .. note::
 
    In Python 2.5, the :keyword:`with` statement is only allowed when the
    ``with_statement`` feature has been enabled.  It is always enabled in
    Python 2.6.
 
+.. versionchanged:: 2.7
+   Support for multiple context expressions.
+
 .. seealso::
 
    :pep:`0343` - The "with" statement