add a SETUP_WITH opcode

It speeds up the with statement and correctly looks up the special
methods involved.

2 files changed, 15 insertions, 1 deletions

diff --git a/Doc/library/dis.rst b/Doc/library/dis.rst
index 6b7ed1e..9bd65dd 100644
--- a/Doc/library/dis.rst
+++ b/Doc/library/dis.rst
@@ -532,6 +532,18 @@ Miscellaneous opcodes.
    the names of the base classes, and TOS2 the class name.
 
 
+.. opcode:: SETUP_WITH (delta)
+
+   This opcode performs several operations before a with block starts.  First,
+   it loads :meth:`~object.__exit__` from the context manager and pushes it onto
+   the stack for later use by :opcode:`WITH_CLEANUP`.  Then,
+   :meth:`~object.__enter__` is called, and a finally block pointing to *delta*
+   is pushed.  Finally, the result of calling the enter method is pushed onto
+   the stack.  The next opcode will either ignore it (:opcode:`POP_TOP`), or
+   store it in (a) variable(s) (:opcode:`STORE_FAST`, :opcode:`STORE_NAME`, or
+   :opcode:`UNPACK_SEQUENCE`).
+
+
 .. opcode:: WITH_CLEANUP ()
 
    Cleans up the stack when a :keyword:`with` statement block exits.  On top of
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst
index 3c716b2..afb7ebc 100644
--- a/Doc/reference/compound_stmts.rst
+++ b/Doc/reference/compound_stmts.rst
@@ -339,6 +339,8 @@ The execution of the :keyword:`with` statement proceeds as follows:
 
 #. The context expression is evaluated to obtain a context manager.
 
+#. The context manager's :meth:`__exit__` is loaded for later use.
+
 #. The context manager's :meth:`__enter__` method is invoked.
 
 #. If a target was included in the :keyword:`with` statement, the return value
@@ -349,7 +351,7 @@ The execution of the :keyword:`with` statement proceeds as follows:
       The :keyword:`with` statement guarantees that if the :meth:`__enter__` method
       returns without an error, then :meth:`__exit__` will always be called. Thus, if
       an error occurs during the assignment to the target list, it will be treated the
-      same as an error occurring within the suite would be. See step 5 below.
+      same as an error occurring within the suite would be. See step 6 below.
 
 #. The suite is executed.