expose PYTHON_API_VERSION macro as sys.api_version. Closes patch # 601456.

Doc/lib/libsys.tex

@@ -459,6 +459,12 @@ else:
 \end{verbatim}
 \end{datadesc}
 
+\begin{datadesc}{api_version}
+  The C API version for this interpreter.  Programmers may find this useful
+  when debugging version conflicts between Python and extension
+  modules. \versionadded{2.3}
+\end{datadesc}
+
 \begin{datadesc}{version_info}
   A tuple containing the five components of the version number:
   \var{major}, \var{minor}, \var{micro}, \var{releaselevel}, and

Misc/NEWS

@@ -303,6 +303,10 @@ Extension modules
 - signal.sigpending, signal.sigprocmask and signal.sigsuspend have
   been added where available.
 
+- The sys module acquired a new attribute, api_version, which evaluates
+  to the value of the PYTHON_API_VERSION macro with which the
+  interpreter was compiled.
+
 Library
 
 - New module: sets, defines the class Set that implements a mutable

Python/sysmodule.c

@@ -793,6 +793,9 @@ _PySys_Init(void)
 					       PY_MICRO_VERSION, s,
 					       PY_RELEASE_SERIAL));
 	Py_XDECREF(v);
+	PyDict_SetItemString(sysdict, "api_version",
+			     v = PyInt_FromLong(PYTHON_API_VERSION));
+	Py_XDECREF(v);
 	PyDict_SetItemString(sysdict, "copyright",
 			     v = PyString_FromString(Py_GetCopyright()));
 	Py_XDECREF(v);