SF patch 576101, by Oren Tirosh: alternative implementation of

interning.  I modified Oren's patch significantly, but the basic idea
and most of the implementation is unchanged.  Interned strings created
with PyString_InternInPlace() are now mortal, and you must keep a
reference to the resulting string around; use the new function
PyString_InternImmortal() to create immortal interned strings.

1 files changed, 17 insertions, 0 deletions

diff --git a/Misc/NEWS b/Misc/NEWS
index d60205e..7034d72 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -57,6 +57,10 @@ Type/class unification and new-style classes
 
 Core and builtins
 
+- A subtle change to the semantics of the built-in function intern():
+  interned strings are no longer immortal.  You must keep a reference
+  to the return value intern() around to get the benefit.
+
 - Use of 'None' as a variable, argument or attribute name now
   issues a SyntaxWarning.  In the future, None may become a keyword.
 
@@ -514,6 +518,19 @@ Build
 
 C API
 
+- The string object's layout has changed: the pointer member
+  ob_sinterned has been replaced by an int member ob_sstate.  On some
+  platforms (e.g. most 64-bit systems) this may change the offset of
+  the ob_sval member, so as a precaution the API_VERSION has been
+  incremented.  The apparently unused feature of "indirect interned
+  strings", supported by the ob_sinterned member, is gone.  Interned
+  strings are now usually mortal; theres a new API,
+  PyString_InternImmortal() that creates immortal interned strings.
+  (The ob_sstate member can only take three values; however, while
+  making it a char saves a few bytes per string object on average, in
+  it also slowed things down a bit because ob_sval was no longer
+  aligned.)
+
 - The Py_InitModule*() functions now accept NULL for the 'methods'
   argument.  Modules without global functions are becoming more common
   now that factories can be types rather than functions.