diff -r 32e795204f1c Include/pyerrors.h
--- a/Include/pyerrors.h	Thu Oct 14 23:15:17 2010 +0200
+++ b/Include/pyerrors.h	Thu Oct 14 23:25:50 2010 +0200
@@ -170,6 +170,7 @@ PyAPI_DATA(PyObject *) PyExc_FutureWarni
 PyAPI_DATA(PyObject *) PyExc_ImportWarning;
 PyAPI_DATA(PyObject *) PyExc_UnicodeWarning;
 PyAPI_DATA(PyObject *) PyExc_BytesWarning;
+PyAPI_DATA(PyObject *) PyExc_ResourceWarning;
 
 
 /* Convenience functions */
diff -r 32e795204f1c Lib/socket.py
--- a/Lib/socket.py	Thu Oct 14 23:15:17 2010 +0200
+++ b/Lib/socket.py	Thu Oct 14 23:25:50 2010 +0200
@@ -108,7 +108,7 @@ class socket(_socket.socket):
         if s.startswith("<socket object"):
             s = "<%s.%s%s%s" % (self.__class__.__module__,
                                 self.__class__.__name__,
-                                (self._closed and " [closed] ") or "",
+                                getattr(self, '_closed', False) and " [closed] " or "",
                                 s[7:])
         return s
 
diff -r 32e795204f1c Lib/test/exception_hierarchy.txt
--- a/Lib/test/exception_hierarchy.txt	Thu Oct 14 23:15:17 2010 +0200
+++ b/Lib/test/exception_hierarchy.txt	Thu Oct 14 23:25:50 2010 +0200
@@ -47,3 +47,4 @@ BaseException
            +-- ImportWarning
            +-- UnicodeWarning
            +-- BytesWarning
+           +-- ResourceWarning
diff -r 32e795204f1c Lib/test/test_io.py
--- a/Lib/test/test_io.py	Thu Oct 14 23:15:17 2010 +0200
+++ b/Lib/test/test_io.py	Thu Oct 14 23:25:50 2010 +0200
@@ -29,6 +29,7 @@ import weakref
 import abc
 import signal
 import errno
+import warnings
 from itertools import cycle, count
 from collections import deque
 from test import support
@@ -2525,6 +2526,46 @@ class MiscIOTest(unittest.TestCase):
         # baseline "io" module.
         self._check_abc_inheritance(io)
 
+    def _check_warn_on_dealloc(self, *args, **kwargs):
+        f = open(*args, **kwargs)
+        r = repr(f)
+        with self.assertWarns(ResourceWarning) as cm:
+            f = None
+            support.gc_collect()
+        self.assertIn(r, str(cm.warning.args[0]))
+
+    def test_warn_on_dealloc(self):
+        self._check_warn_on_dealloc(support.TESTFN, "wb", buffering=0)
+        self._check_warn_on_dealloc(support.TESTFN, "wb")
+        self._check_warn_on_dealloc(support.TESTFN, "w")
+
+    def _check_warn_on_dealloc_fd(self, *args, **kwargs):
+        fds = []
+        try:
+            r, w = os.pipe()
+            fds += r, w
+            self._check_warn_on_dealloc(r, *args, **kwargs)
+            # When using closefd=False, there's no warning
+            r, w = os.pipe()
+            fds += r, w
+            with warnings.catch_warnings(record=True) as recorded:
+                open(r, *args, closefd=False, **kwargs)
+                support.gc_collect()
+            self.assertEqual(recorded, [])
+        finally:
+            for fd in fds:
+                try:
+                    os.close(fd)
+                except EnvironmentError as e:
+                    if e.errno != errno.EBADF:
+                        raise
+
+    def test_warn_on_dealloc_fd(self):
+        self._check_warn_on_dealloc_fd("rb", buffering=0)
+        self._check_warn_on_dealloc_fd("rb")
+        self._check_warn_on_dealloc_fd("r")
+
+
 class CMiscIOTest(MiscIOTest):
     io = io
 
diff -r 32e795204f1c Lib/test/test_socket.py
--- a/Lib/test/test_socket.py	Thu Oct 14 23:15:17 2010 +0200
+++ b/Lib/test/test_socket.py	Thu Oct 14 23:25:50 2010 +0200
@@ -695,6 +695,23 @@ class GeneralModuleTests(unittest.TestCa
     def test_sendall_interrupted_with_timeout(self):
         self.check_sendall_interrupted(True)
 
+    def test_dealloc_warn(self):
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        r = repr(sock)
+        with self.assertWarns(ResourceWarning) as cm:
+            sock = None
+            support.gc_collect()
+        self.assertIn(r, str(cm.warning.args[0]))
+        # An open socket file object gets dereferenced after the socket
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        f = sock.makefile('rb')
+        r = repr(sock)
+        sock = None
+        support.gc_collect()
+        with self.assertWarns(ResourceWarning):
+            f = None
+            support.gc_collect()
+
 
 @unittest.skipUnless(thread, 'Threading required for this test.')
 class BasicTCPTest(SocketConnectedTest):
diff -r 32e795204f1c Lib/warnings.py
--- a/Lib/warnings.py	Thu Oct 14 23:15:17 2010 +0200
+++ b/Lib/warnings.py	Thu Oct 14 23:25:50 2010 +0200
@@ -383,4 +383,10 @@ if not _warnings_defaults:
     else:
         bytes_action = "ignore"
     simplefilter(bytes_action, category=BytesWarning, append=1)
+    # Resource consumption warnings are enabled by default in pydebug mode
+    if hasattr(sys, 'gettotalrefcount'):
+        resource_action = "always"
+    else:
+        resource_action = "ignore"
+    simplefilter(resource_action, category=ResourceWarning, append=1)
 del _warnings_defaults
diff -r 32e795204f1c Lib/xml/etree/ElementTree.py
--- a/Lib/xml/etree/ElementTree.py	Thu Oct 14 23:15:17 2010 +0200
+++ b/Lib/xml/etree/ElementTree.py	Thu Oct 14 23:25:50 2010 +0200
@@ -662,17 +662,23 @@ class ElementTree:
     # @exception ParseError If the parser fails to parse the document.
 
     def parse(self, source, parser=None):
+        close_source = False
         if not hasattr(source, "read"):
             source = open(source, "rb")
-        if not parser:
-            parser = XMLParser(target=TreeBuilder())
-        while 1:
-            data = source.read(65536)
-            if not data:
-                break
-            parser.feed(data)
-        self._root = parser.close()
-        return self._root
+            close_source = True
+        try:
+            if not parser:
+                parser = XMLParser(target=TreeBuilder())
+            while 1:
+                data = source.read(65536)
+                if not data:
+                    break
+                parser.feed(data)
+            self._root = parser.close()
+            return self._root
+        finally:
+            if close_source:
+                source.close()
 
     ##
     # Creates a tree iterator for the root element.  The iterator loops
@@ -1226,16 +1232,19 @@ def parse(source, parser=None):
 # @return A (event, elem) iterator.
 
 def iterparse(source, events=None, parser=None):
+    close_source = False
     if not hasattr(source, "read"):
         source = open(source, "rb")
+        close_source = True
     if not parser:
         parser = XMLParser(target=TreeBuilder())
-    return _IterParseIterator(source, events, parser)
+    return _IterParseIterator(source, events, parser, close_source)
 
 class _IterParseIterator:
 
-    def __init__(self, source, events, parser):
+    def __init__(self, source, events, parser, close_source=False):
         self._file = source
+        self._close_file = close_source
         self._events = []
         self._index = 0
         self.root = self._root = None
@@ -1282,6 +1291,8 @@ class _IterParseIterator:
             except IndexError:
                 if self._parser is None:
                     self.root = self._root
+                    if self._close_file:
+                        self._file.close()
                     raise StopIteration
                 # load event buffer
                 del self._events[:]
diff -r 32e795204f1c Modules/_elementtree.c
--- a/Modules/_elementtree.c	Thu Oct 14 23:15:17 2010 +0200
+++ b/Modules/_elementtree.c	Thu Oct 14 23:25:50 2010 +0200
@@ -2946,19 +2946,25 @@ PyInit__elementtree(void)
 
         "class ElementTree(ET.ElementTree):\n" /* public */
         "  def parse(self, source, parser=None):\n"
+        "    close_source = False\n"
         "    if not hasattr(source, 'read'):\n"
         "      source = open(source, 'rb')\n"
-        "    if parser is not None:\n"
-        "      while 1:\n"
-        "        data = source.read(65536)\n"
-        "        if not data:\n"
-        "          break\n"
-        "        parser.feed(data)\n"
-        "      self._root = parser.close()\n"
-        "    else:\n" 
-        "      parser = cElementTree.XMLParser()\n"
-        "      self._root = parser._parse(source)\n"
-        "    return self._root\n"
+        "      close_source = True\n"
+        "    try:\n"
+        "      if parser is not None:\n"
+        "        while 1:\n"
+        "          data = source.read(65536)\n"
+        "          if not data:\n"
+        "            break\n"
+        "          parser.feed(data)\n"
+        "        self._root = parser.close()\n"
+        "      else:\n" 
+        "        parser = cElementTree.XMLParser()\n"
+        "        self._root = parser._parse(source)\n"
+        "      return self._root\n"
+        "    finally:\n"
+        "      if close_source:\n"
+        "        source.close()\n"
         "cElementTree.ElementTree = ElementTree\n"
 
         "def iter(node, tag=None):\n" /* helper */
@@ -2988,8 +2994,10 @@ PyInit__elementtree(void)
         "class iterparse:\n"
         " root = None\n"
         " def __init__(self, file, events=None):\n"
+        "  self._close_file = False\n"
         "  if not hasattr(file, 'read'):\n"
         "    file = open(file, 'rb')\n"
+        "    self._close_file = True\n"
         "  self._file = file\n"
         "  self._events = []\n"
         "  self._index = 0\n"
@@ -3004,6 +3012,8 @@ PyInit__elementtree(void)
         "    except IndexError:\n"
         "      if self._parser is None:\n"
         "        self.root = self._root\n"
+        "        if self._close_file:\n"
+        "          self._file.close()\n"
         "        raise StopIteration\n"
         "      # load event buffer\n"
         "      del self._events[:]\n"
diff -r 32e795204f1c Modules/_io/bufferedio.c
--- a/Modules/_io/bufferedio.c	Thu Oct 14 23:15:17 2010 +0200
+++ b/Modules/_io/bufferedio.c	Thu Oct 14 23:25:50 2010 +0200
@@ -197,6 +197,7 @@ typedef struct {
     int detached;
     int readable;
     int writable;
+    int deallocating;
     
     /* True if this is a vanilla Buffered object (rather than a user derived
        class) *and* the raw stream is a vanilla FileIO object. */
@@ -342,6 +343,7 @@ typedef struct {
 static void
 buffered_dealloc(buffered *self)
 {
+    self->deallocating = 1;
     if (self->ok && _PyIOBase_finalize((PyObject *) self) < 0)
         return;
     _PyObject_GC_UNTRACK(self);
@@ -382,6 +384,23 @@ buffered_clear(buffered *self)
     return 0;
 }
 
+/* Because this can call arbitrary code, it shouldn't be called when
+   the refcount is 0 (that is, not directly from tp_dealloc unless
+   the refcount has been temporarily re-incremented). */
+PyObject *
+buffered_dealloc_warn(buffered *self, PyObject *source)
+{
+    if (self->ok && self->raw) {
+        PyObject *r;
+        r = PyObject_CallMethod(self->raw, "_dealloc_warn", "O", source);
+        if (r)
+            Py_DECREF(r);
+        else
+            PyErr_Clear();
+    }
+    Py_RETURN_NONE;
+}
+
 /*
  * _BufferedIOMixin methods
  * This is not a class, just a collection of methods that will be reused
@@ -435,6 +454,14 @@ buffered_close(buffered *self, PyObject 
         Py_INCREF(res);
         goto end;
     }
+
+    if (self->deallocating) {
+        PyObject *r = buffered_dealloc_warn(self, (PyObject *) self);
+        if (r)
+            Py_DECREF(r);
+        else
+            PyErr_Clear();
+    }
     /* flush() will most probably re-take the lock, so drop it first */
     LEAVE_BUFFERED(self)
     res = PyObject_CallMethodObjArgs((PyObject *)self, _PyIO_str_flush, NULL);
@@ -1461,6 +1488,7 @@ static PyMethodDef bufferedreader_method
     {"writable", (PyCFunction)buffered_writable, METH_NOARGS},
     {"fileno", (PyCFunction)buffered_fileno, METH_NOARGS},
     {"isatty", (PyCFunction)buffered_isatty, METH_NOARGS},
+    {"_dealloc_warn", (PyCFunction)buffered_dealloc_warn, METH_O},
 
     {"read", (PyCFunction)buffered_read, METH_VARARGS},
     {"peek", (PyCFunction)buffered_peek, METH_VARARGS},
@@ -1843,6 +1871,7 @@ static PyMethodDef bufferedwriter_method
     {"writable", (PyCFunction)buffered_writable, METH_NOARGS},
     {"fileno", (PyCFunction)buffered_fileno, METH_NOARGS},
     {"isatty", (PyCFunction)buffered_isatty, METH_NOARGS},
+    {"_dealloc_warn", (PyCFunction)buffered_dealloc_warn, METH_O},
 
     {"write", (PyCFunction)bufferedwriter_write, METH_VARARGS},
     {"truncate", (PyCFunction)buffered_truncate, METH_VARARGS},
@@ -2227,6 +2256,7 @@ static PyMethodDef bufferedrandom_method
     {"writable", (PyCFunction)buffered_writable, METH_NOARGS},
     {"fileno", (PyCFunction)buffered_fileno, METH_NOARGS},
     {"isatty", (PyCFunction)buffered_isatty, METH_NOARGS},
+    {"_dealloc_warn", (PyCFunction)buffered_dealloc_warn, METH_O},
 
     {"flush", (PyCFunction)buffered_flush, METH_NOARGS},
 
@@ -2296,4 +2326,3 @@ PyTypeObject PyBufferedRandom_Type = {
     0,                          /* tp_alloc */
     PyType_GenericNew,          /* tp_new */
 };
-
diff -r 32e795204f1c Modules/_io/fileio.c
--- a/Modules/_io/fileio.c	Thu Oct 14 23:15:17 2010 +0200
+++ b/Modules/_io/fileio.c	Thu Oct 14 23:25:50 2010 +0200
@@ -2,6 +2,7 @@
 
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
+#include "structmember.h"
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
 #endif
@@ -55,6 +56,7 @@ typedef struct {
     unsigned int writable : 1;
     signed int seekable : 2; /* -1 means unknown */
     unsigned int closefd : 1;
+    unsigned int deallocating: 1;
     PyObject *weakreflist;
     PyObject *dict;
 } fileio;
@@ -69,6 +71,26 @@ _PyFileIO_closed(PyObject *self)
     return ((fileio *)self)->fd < 0;
 }
 
+/* Because this can call arbitrary code, it shouldn't be called when
+   the refcount is 0 (that is, not directly from tp_dealloc unless
+   the refcount has been temporarily re-incremented). */
+static PyObject *
+fileio_dealloc_warn(fileio *self, PyObject *source)
+{
+    if (self->fd >= 0 && self->closefd) {
+        PyObject *exc, *val, *tb;
+        PyErr_Fetch(&exc, &val, &tb);
+        if (PyErr_WarnFormat(PyExc_ResourceWarning, 1,
+                             "unclosed file %R", source)) {
+            /* Spurious errors can appear at shutdown */
+            if (PyErr_ExceptionMatches(PyExc_Warning))
+                PyErr_WriteUnraisable((PyObject *) self);
+        }
+        PyErr_Restore(exc, val, tb);
+    }
+    Py_RETURN_NONE;
+}
+
 static PyObject *
 portable_lseek(int fd, PyObject *posobj, int whence);
 
@@ -110,6 +132,13 @@ fileio_close(fileio *self)
         self->fd = -1;
         Py_RETURN_NONE;
     }
+    if (self->deallocating) {
+        PyObject *r = fileio_dealloc_warn(self, (PyObject *) self);
+        if (r)
+            Py_DECREF(r);
+        else
+            PyErr_Clear();
+    }
     errno = internal_close(self);
     if (errno < 0)
         return NULL;
@@ -398,6 +427,7 @@ fileio_clear(fileio *self)
 static void
 fileio_dealloc(fileio *self)
 {
+    self->deallocating = 1;
     if (_PyIOBase_finalize((PyObject *) self) < 0)
         return;
     _PyObject_GC_UNTRACK(self);
@@ -1007,6 +1037,7 @@ static PyMethodDef fileio_methods[] = {
     {"writable", (PyCFunction)fileio_writable, METH_NOARGS,      writable_doc},
     {"fileno",   (PyCFunction)fileio_fileno,   METH_NOARGS,      fileno_doc},
     {"isatty",   (PyCFunction)fileio_isatty,   METH_NOARGS,      isatty_doc},
+    {"_dealloc_warn", (PyCFunction)fileio_dealloc_warn, METH_O, NULL},
     {NULL,           NULL}             /* sentinel */
 };
 
diff -r 32e795204f1c Modules/_io/textio.c
--- a/Modules/_io/textio.c	Thu Oct 14 23:15:17 2010 +0200
+++ b/Modules/_io/textio.c	Thu Oct 14 23:25:50 2010 +0200
@@ -658,6 +658,7 @@ typedef struct
     char writetranslate;
     char seekable;
     char telling;
+    char deallocating;
     /* Specialized encoding func (see below) */
     encodefunc_t encodefunc;
     /* Whether or not it's the start of the stream */
@@ -1094,6 +1095,7 @@ _textiowrapper_clear(textio *self)
 static void
 textiowrapper_dealloc(textio *self)
 {
+    self->deallocating = 1;
     if (_textiowrapper_clear(self) < 0)
         return;
     _PyObject_GC_UNTRACK(self);
@@ -2410,6 +2412,13 @@ textiowrapper_close(textio *self, PyObje
         Py_RETURN_NONE; /* stream already closed */
     }
     else {
+        if (self->deallocating) {
+            res = PyObject_CallMethod(self->buffer, "_dealloc_warn", "O", self);
+            if (res)
+                Py_DECREF(res);
+            else
+                PyErr_Clear();
+        }
         res = PyObject_CallMethod((PyObject *)self, "flush", NULL);
         if (res == NULL) {
             return NULL;
diff -r 32e795204f1c Modules/socketmodule.c
--- a/Modules/socketmodule.c	Thu Oct 14 23:15:17 2010 +0200
+++ b/Modules/socketmodule.c	Thu Oct 14 23:25:50 2010 +0200
@@ -2931,8 +2931,20 @@ static PyMemberDef sock_memberlist[] = {
 static void
 sock_dealloc(PySocketSockObject *s)
 {
-    if (s->sock_fd != -1)
+    if (s->sock_fd != -1) {
+        PyObject *exc, *val, *tb;
+        Py_ssize_t old_refcount = Py_REFCNT(s);
+        Py_INCREF(s);
+        PyErr_Fetch(&exc, &val, &tb);
+        if (PyErr_WarnFormat(PyExc_ResourceWarning, 1,
+                             "unclosed %R", s))
+            /* Spurious errors can appear at shutdown */
+            if (PyErr_ExceptionMatches(PyExc_Warning))
+                PyErr_WriteUnraisable((PyObject *) s);
+        PyErr_Restore(exc, val, tb);
         (void) SOCKETCLOSE(s->sock_fd);
+        Py_REFCNT(s) = old_refcount;
+    }
     Py_TYPE(s)->tp_free((PyObject *)s);
 }
 
diff -r 32e795204f1c Objects/exceptions.c
--- a/Objects/exceptions.c	Thu Oct 14 23:15:17 2010 +0200
+++ b/Objects/exceptions.c	Thu Oct 14 23:25:50 2010 +0200
@@ -1831,6 +1831,13 @@ SimpleExtendsException(PyExc_Warning, Ru
 
 
 /*
+ *    ResourceWarning extends Warning
+ */
+SimpleExtendsException(PyExc_Warning, ResourceWarning,
+                       "Base class for warnings about resource usage.");
+
+
+/*
  *    FutureWarning extends Warning
  */
 SimpleExtendsException(PyExc_Warning, FutureWarning,
@@ -1935,6 +1942,7 @@ _PyExc_Init(void)
     PRE_INIT(PendingDeprecationWarning)
     PRE_INIT(SyntaxWarning)
     PRE_INIT(RuntimeWarning)
+    PRE_INIT(ResourceWarning)
     PRE_INIT(FutureWarning)
     PRE_INIT(ImportWarning)
     PRE_INIT(UnicodeWarning)
@@ -1997,6 +2005,7 @@ _PyExc_Init(void)
     POST_INIT(PendingDeprecationWarning)
     POST_INIT(SyntaxWarning)
     POST_INIT(RuntimeWarning)
+    POST_INIT(ResourceWarning)
     POST_INIT(FutureWarning)
     POST_INIT(ImportWarning)
     POST_INIT(UnicodeWarning)
diff -r 32e795204f1c Python/_warnings.c
--- a/Python/_warnings.c	Thu Oct 14 23:15:17 2010 +0200
+++ b/Python/_warnings.c	Thu Oct 14 23:25:50 2010 +0200
@@ -835,6 +835,7 @@ create_filter(PyObject *category, const 
     static PyObject *ignore_str = NULL;
     static PyObject *error_str = NULL;
     static PyObject *default_str = NULL;
+    static PyObject *always_str = NULL;
     PyObject *action_obj = NULL;
     PyObject *lineno, *result;
 
@@ -862,6 +863,14 @@ create_filter(PyObject *category, const 
         }
         action_obj = default_str;
     }
+    else if (!strcmp(action, "always")) {
+        if (always_str == NULL) {
+            always_str = PyUnicode_InternFromString("always");
+            if (always_str == NULL)
+                return NULL;
+        }
+        action_obj = always_str;
+    }
     else {
         Py_FatalError("unknown action");
     }
@@ -879,10 +888,10 @@ static PyObject *
 init_filters(void)
 {
     /* Don't silence DeprecationWarning if -3 was used. */
-    PyObject *filters = PyList_New(4);
+    PyObject *filters = PyList_New(5);
     unsigned int pos = 0;  /* Post-incremented in each use. */
     unsigned int x;
-    const char *bytes_action;
+    const char *bytes_action, *resource_action;
 
     if (filters == NULL)
         return NULL;
@@ -901,6 +910,13 @@ init_filters(void)
         bytes_action = "ignore";
     PyList_SET_ITEM(filters, pos++, create_filter(PyExc_BytesWarning,
                     bytes_action));
+#ifdef Py_DEBUG
+    resource_action = "always";
+#else
+    resource_action = "ignore";
+#endif
+    PyList_SET_ITEM(filters, pos++, create_filter(PyExc_ResourceWarning,
+                    resource_action));
 
     for (x = 0; x < pos; x += 1) {
         if (PyList_GET_ITEM(filters, x) == NULL) {