Add a stream parameter to gc.set_debug

Modules/gcmodule.c

Index: Modules/gcmodule.c
===================================================================
--- Modules/gcmodule.c	(revision 74542)
+++ Modules/gcmodule.c	(working copy)
@@ -127,6 +127,12 @@
 static int debug;
 static PyObject *tmod = NULL;
 
+/* 
+   Defines where debugging output is written. 
+   Should be a write(str) callable. If NULL, output is written to stderr.
+*/ 
+static PyObject* debug_writer = NULL;
+
 /*--------------------------------------------------------------------------
 gc_refs values.
 
@@ -689,6 +695,25 @@
 }
 
 static void
+debug_print(const char* format, ...)
+{
+    va_list va;
+
+    va_start(va, format);
+
+    if (debug_writer == NULL) PySys_WriteStderr(format, va);
+    else {
+        
+        PyObject* msg = PyString_FromFormatV(format, va);
+        if (NULL == PyObject_CallFunctionObjArgs(debug_writer, msg, NULL))
+            PyErr_WriteUnraisable(debug_writer);
+            
+        Py_DECREF(msg);
+    }
+    va_end(va);
+}
+
+static void
 debug_instance(char *msg, PyInstanceObject *inst)
 {
 	char *cname;
@@ -698,7 +723,7 @@
 		cname = PyString_AsString(classname);
 	else
 		cname = "?";
-	PySys_WriteStderr("gc: %.100s <%.100s instance at %p>\n",
+	debug_print("gc: %.100s <%.100s instance at %p>\n",
 			  msg, cname, inst);
 }
 
@@ -709,7 +734,7 @@
 		debug_instance(msg, (PyInstanceObject *)op);
 	}
 	else if (debug & DEBUG_OBJECTS) {
-		PySys_WriteStderr("gc: %.100s <%.100s %p>\n",
+		debug_print("gc: %.100s <%.100s %p>\n",
 				  msg, Py_TYPE(op)->tp_name, op);
 	}
 }
@@ -838,13 +863,13 @@
 
 	if (debug & DEBUG_STATS) {
 		t1 = get_time();
-		PySys_WriteStderr("gc: collecting generation %d...\n",
+		debug_print("gc: collecting generation %d...\n",
 				  generation);
-		PySys_WriteStderr("gc: objects in each generation:");
+		debug_print("gc: objects in each generation:");
 		for (i = 0; i < NUM_GENERATIONS; i++)
-			PySys_WriteStderr(" %" PY_FORMAT_SIZE_T "d",
+			debug_print(" %" PY_FORMAT_SIZE_T "d",
 					  gc_list_size(GEN_HEAD(i)));
-		PySys_WriteStderr("\n");
+		debug_print("\n");
 	}
 
 	/* update collection and allocation counters */
@@ -941,17 +966,17 @@
 	if (debug & DEBUG_STATS) {
 		double t2 = get_time();
 		if (m == 0 && n == 0)
-			PySys_WriteStderr("gc: done");
+			debug_print("gc: done");
 		else
-			PySys_WriteStderr(
+			debug_print(
 			    "gc: done, "
 			    "%" PY_FORMAT_SIZE_T "d unreachable, "
 			    "%" PY_FORMAT_SIZE_T "d uncollectable",
 			    n+m, n);
 		if (t1 && t2) {
-			PySys_WriteStderr(", %.4fs elapsed", t2-t1);
+			debug_print(", %.4fs elapsed", t2-t1);
 		}
-		PySys_WriteStderr(".\n");
+		debug_print(".\n");
 	}
 
 	/* Append instances in the uncollectable set to a Python
@@ -1072,7 +1097,7 @@
 }
 
 PyDoc_STRVAR(gc_set_debug__doc__,
-"set_debug(flags) -> None\n"
+"set_debug(flags[, stream=sys.stderr]) -> None\n"
 "\n"
 "Set the garbage collection debugging flags. Debugging information is\n"
 "written to sys.stderr.\n"
@@ -1085,14 +1110,41 @@
 "  DEBUG_INSTANCES - Print instance objects.\n"
 "  DEBUG_OBJECTS - Print objects other than instances.\n"
 "  DEBUG_SAVEALL - Save objects to gc.garbage rather than freeing them.\n"
-"  DEBUG_LEAK - Debug leaking programs (everything but STATS).\n");
+"  DEBUG_LEAK - Debug leaking programs (everything but STATS).\n"
+"\n"
+"stream is a file object to which debugging output will be written.\n");
 
 static PyObject *
 gc_set_debug(PyObject *self, PyObject *args)
 {
-	if (!PyArg_ParseTuple(args, "i:set_debug", &debug))
+    PyObject* stream = NULL;
+    int flags;
+
+	if (!PyArg_ParseTuple(args, "i|O:set_debug", &flags, &stream))
 		return NULL;
 
+    PyObject* writer = NULL;
+    if (stream != NULL) {
+        /* Be defensive, we don't want errors to occur during collection */
+        writer = PyObject_GetAttrString(stream, "write");
+        if (writer == NULL)
+            return NULL;
+
+        if (!PyCallable_Check(writer)) {
+            PyErr_SetString(PyExc_TypeError,
+                "attribute write of parameter stream must be callable");
+            return NULL;
+        }
+
+    }
+
+    if (debug_writer != NULL) {
+        Py_DECREF(debug_writer);
+        debug_writer = NULL;
+    }
+    debug_writer = writer;
+    debug = flags;
+
 	Py_INCREF(Py_None);
 	return Py_None;
 }