Index: Python/sysmodule.c
===================================================================
--- Python/sysmodule.c	(revision 86100)
+++ Python/sysmodule.c	(working copy)
@@ -67,7 +67,25 @@
         return PyDict_SetItemString(sd, name, v);
 }
 
+#ifdef Py_BREAKPOINT
+PyDoc_STRVAR(breakpoint_doc,
+"_breakpoint(args) -> None\n"
+"\n"
+"Inject a breakpoint signal in this process, for use when running CPython\n"
+"under a debugger.\n"
+"Note that invoking this when running outside of a C-level debugger is likely\n"
+"to make the process terminate\n"
+);
+
 static PyObject *
+sys_breakpoint(PyObject *self, PyObject *args)
+{
+    Py_BREAKPOINT();
+    Py_RETURN_NONE;
+}
+#endif /* Py_BREAKPOINT */
+
+static PyObject *
 sys_displayhook(PyObject *self, PyObject *o)
 {
     PyObject *outf;
@@ -949,6 +967,9 @@
 
 static PyMethodDef sys_methods[] = {
     /* Might as well keep this in alphabetic order */
+#ifdef Py_BREAKPOINT
+    {"_breakpoint", sys_breakpoint, METH_VARARGS, breakpoint_doc},
+#endif
     {"callstats", (PyCFunction)PyEval_GetCallStats, METH_NOARGS,
      callstats_doc},
     {"_clear_type_cache",       sys_clear_type_cache,     METH_NOARGS,
Index: Include/pyport.h
===================================================================
--- Include/pyport.h	(revision 86100)
+++ Include/pyport.h	(working copy)
@@ -836,4 +836,13 @@
 #endif
 #endif
 
+/*
+ * System-dependent ways of injecting a breakpoint:
+ */
+#if defined(MS_WINDOWS) && defined(_DEBUG)
+#  define Py_BREAKPOINT()  DebugBreak()
+#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64))
+#  define Py_BREAKPOINT()  __asm__ __volatile__ ("int $03")
+#endif
+
 #endif /* Py_PYPORT_H */
Index: Doc/library/sys.rst
===================================================================
--- Doc/library/sys.rst	(revision 86100)
+++ Doc/library/sys.rst	(working copy)
@@ -29,6 +29,31 @@
    command line, see the :mod:`fileinput` module.
 
 
+.. function:: _breakpoint(args)
+
+   .. impl-detail::
+      This function is only meaningful for the CPython implementation of Python
+      and thus not likely to be implemented elsewhere.  It is only present on
+      builds of CPython in which the necessary system-dependent hooks are
+      available.
+
+   This function is for use when debugging CPython (and extension modules).
+   When running CPython under a C debugger, it injects a C-level breakpoint,
+   stopping execution at this point.  *args* can be arbitrary user-supplied
+   objects, which should be viewable within the debugger.
+
+   This may be of use when tracking down bugs: the breakpoint can be guarded
+   by Python-level conditionals::
+
+       if foo and bar and not baz:
+          sys._breakpoint(some_func(foo, bar, baz))
+
+   When running CPython outside of a debugger, this will typically terminate
+   the process immediately, so remember not to leave these breakpoints in your
+   final code.
+
+   .. versionadded:: 3.2
+
 .. data:: byteorder
 
    An indicator of the native byte order.  This will have the value ``'big'`` on
Index: Lib/test/test_sys.py
===================================================================
--- Lib/test/test_sys.py	(revision 86100)
+++ Lib/test/test_sys.py	(working copy)
@@ -862,8 +862,37 @@
         check(sys.flags, size(vh) + self.P * len(sys.flags))
 
 
+class BreakpointTest(unittest.TestCase):
+    def test_sys_breakpoint(self):
+        try:
+            gdb_version, _ = subprocess.Popen(["gdb", "--version"],
+                                              stdout=subprocess.PIPE).communicate()
+        except OSError:
+            # This is what "no gdb" looks like.  There may, however, be other
+            # errors that manifest this way too.
+            raise unittest.SkipTest("Couldn't find gdb on the path")
+
+        # Run "sys._breakpoint" under gdb in a subprocess:
+        commands = ['run', 'bt', 'print args']
+        args = ["gdb", "--batch"]
+        args += ['--eval-command=%s' % cmd for cmd in commands]
+        args += ["--args",
+                 sys.executable,
+                 '-c',
+                 'import sys; sys._breakpoint(42)']
+        out, err = subprocess.Popen(
+            args, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+            ).communicate()
+        out = out.decode('utf-8', 'replace')
+        err = err.decode('utf-8', 'replace')
+        self.assertEquals(err, '')
+        self.assertIn('Program received signal SIGTRAP, '
+                      'Trace/breakpoint trap.', out)
+        self.assertIn('sys_breakpoint', out)
+        self.assertIn('Python/sysmodule.c', out)
+
 def test_main():
-    test.support.run_unittest(SysModuleTest, SizeofTest)
+    test.support.run_unittest(SysModuleTest, SizeofTest, BreakpointTest)
 
 if __name__ == "__main__":
     test_main()