Index: Python/_warnings.c
===================================================================
--- Python/_warnings.c	(revision 77294)
+++ Python/_warnings.c	(working copy)
@@ -839,26 +839,29 @@
 static PyObject *
 init_filters(void)
 {
-    PyObject *filters = PyList_New(3);
+    PyObject *filters = PyList_New(4);
     const char *bytes_action;
     if (filters == NULL)
         return NULL;
 
     PyList_SET_ITEM(filters, 0,
+		    create_filter(PyExc_DeprecationWarning, "ignore"));
+    PyList_SET_ITEM(filters, 1,
                     create_filter(PyExc_PendingDeprecationWarning, "ignore"));
-    PyList_SET_ITEM(filters, 1, create_filter(PyExc_ImportWarning, "ignore"));
+    PyList_SET_ITEM(filters, 2, create_filter(PyExc_ImportWarning, "ignore"));
     if (Py_BytesWarningFlag > 1)
         bytes_action = "error";
     else if (Py_BytesWarningFlag)
         bytes_action = "default";
     else
         bytes_action = "ignore";
-    PyList_SET_ITEM(filters, 2, create_filter(PyExc_BytesWarning,
+    PyList_SET_ITEM(filters, 3, create_filter(PyExc_BytesWarning,
                     bytes_action));
 
     if (PyList_GET_ITEM(filters, 0) == NULL ||
         PyList_GET_ITEM(filters, 1) == NULL ||
-        PyList_GET_ITEM(filters, 2) == NULL) {
+        PyList_GET_ITEM(filters, 2) == NULL ||
+	PyList_GET_ITEM(filters, 3) == NULL) {
         Py_DECREF(filters);
         return NULL;
     }
Index: Doc/library/warnings.rst
===================================================================
--- Doc/library/warnings.rst	(revision 77294)
+++ Doc/library/warnings.rst	(working copy)
@@ -59,7 +59,7 @@
 | :exc:`UserWarning`               | The default category for :func:`warn`.        |
 +----------------------------------+-----------------------------------------------+
 | :exc:`DeprecationWarning`        | Base category for warnings about deprecated   |
-|                                  | features.                                     |
+|                                  | features (ignored by default).                |
 +----------------------------------+-----------------------------------------------+
 | :exc:`SyntaxWarning`             | Base category for warnings about dubious      |
 |                                  | syntactic features.                           |
@@ -89,7 +89,10 @@
 standard warning categories.  A warning category must always be a subclass of
 the :exc:`Warning` class.
 
+.. versionchanged:: 2.7
+   :exc:`DeprecationWarning` is ignored by default.
 
+
 .. _warning-filter:
 
 The Warnings Filter
@@ -148,15 +151,7 @@
 :mod:`warnings` module parses these when it is first imported (invalid options
 are ignored, after printing a message to ``sys.stderr``).
 
-The warnings that are ignored by default may be enabled by passing :option:`-Wd`
-to the interpreter. This enables default handling for all warnings, including
-those that are normally ignored by default. This is particular useful for
-enabling ImportWarning when debugging problems importing a developed package.
-ImportWarning can also be enabled explicitly in Python code using::
 
-   warnings.simplefilter('default', ImportWarning)
-
-
 .. _warning-suppress:
 
 Temporarily Suppressing Warnings
@@ -226,6 +221,44 @@
 entries from the warnings list before each new operation).
 
 
+Updating Code For New Versions of Python
+----------------------------------------
+
+By default, the Python interpreter ignores warnings that are only of interest
+to developers. This is for two reasons. One is that a developer does not
+necessarily have control over what interpreter a user uses to run their code. It is
+possible that a new version of Python will be released between your release
+cycles that introduces new warnings that your code triggers, e.g. :exc:`DeprecationWarning`
+for a module that you are using. While you as a developer care that your code
+is using a deprecated module, a user does not and thus has no need to see
+this warning simply because they chose to run your code with a new interpreter.
+
+There is also the issue that warnings in Python are triggered during every
+execution. For compiled languages certain warnings only show up once when code
+is compiled into a binary. But because Python is an interpreted language, code
+is essentially "compiled" every time it is run, leading to warnings that a
+compiled language would emit only once to be emitted every time.
+Once again, these types of warnings are of no interest to a user and thus are
+silent by default.
+
+But as these warnings are of interest to developers, you 
+should make sure to test your code without ignoring warnings. From the
+command-line you can enable warnings that are ignored by default by passing :option:`-Wd`
+to the interpreter (this is shorthand for :option:`-W default`).
+This enables default handling for all warnings, including those that are ignored by default.
+To change what action is taken you simply change what argument is passed to
+:option:`-W`, e.g. :option:`-W error`. See the :option:`-W` flag for more
+details on what is possible.
+
+To programmatically do the same as :option:`-Wd`, use::
+
+  warnings.simplefilter('default')
+
+Make sure to execute this code as soon as possible. This prevents the
+registering of what warnings have been raised from unexpectedly influencing how
+future warnings are treated.
+
+
 .. _warning-functions:
 
 Available Functions
Index: Lib/warnings.py
===================================================================
--- Lib/warnings.py	(revision 77294)
+++ Lib/warnings.py	(working copy)
@@ -383,8 +383,8 @@
 # Module initialization
 _processoptions(sys.warnoptions)
 if not _warnings_defaults:
-    simplefilter("ignore", category=PendingDeprecationWarning, append=1)
-    simplefilter("ignore", category=ImportWarning, append=1)
+    for cls in (DeprecationWarning, PendingDeprecationWarning, ImportWarning):
+        simplefilter("ignore", category=cls, append=1)
     bytes_warning = sys.flags.bytes_warning
     if bytes_warning > 1:
         bytes_action = "error"