diff --git a/Doc/library/doctest.rst b/Doc/library/doctest.rst
index 6138e30..28df49c 100644
--- a/Doc/library/doctest.rst
+++ b/Doc/library/doctest.rst
@@ -278,6 +278,10 @@
 Any classes found are recursively searched similarly, to test docstrings in
 their contained methods and nested classes.
 
+.. impl-detail::
+   Prior to version 3.4, extension modules written in C were not fully
+   searched by doctest.
+
 
 .. _doctest-finding-examples:
 
@@ -1285,9 +1289,8 @@
 
    A processing class used to extract the :class:`DocTest`\ s that are relevant to
    a given object, from its docstring and the docstrings of its contained objects.
-   :class:`DocTest`\ s can currently be extracted from the following object types:
-   modules, functions, classes, methods, staticmethods, classmethods, and
-   properties.
+   :class:`DocTest`\ s can be extracted from modules, classes, functions,
+   methods, staticmethods, classmethods, and properties.
 
    The optional argument *verbose* can be used to display the objects searched by
    the finder.  It defaults to ``False`` (no output).
diff --git a/Lib/doctest.py b/Lib/doctest.py
index 7836fd2..ee4e068 100644
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -918,6 +918,8 @@
             return module is inspect.getmodule(object)
         elif inspect.isfunction(object):
             return module.__dict__ is object.__globals__
+        elif inspect.ismethoddescriptor(object):
+            return module.__name__ == object.__objclass__.__module__
         elif inspect.isclass(object):
             return module.__name__ == object.__module__
         elif hasattr(object, '__module__'):
@@ -950,7 +952,7 @@
             for valname, val in obj.__dict__.items():
                 valname = '%s.%s' % (name, valname)
                 # Recurse to functions & classes.
-                if ((inspect.isfunction(val) or inspect.isclass(val)) and
+                if ((inspect.isroutine(val) or inspect.isclass(val)) and
                     self._from_module(module, val)):
                     self._find(tests, val, valname, module, source_lines,
                                globs, seen)
@@ -962,9 +964,8 @@
                     raise ValueError("DocTestFinder.find: __test__ keys "
                                      "must be strings: %r" %
                                      (type(valname),))
-                if not (inspect.isfunction(val) or inspect.isclass(val) or
-                        inspect.ismethod(val) or inspect.ismodule(val) or
-                        isinstance(val, str)):
+                if not (inspect.isroutine(val) or inspect.isclass(val) or
+                        inspect.ismodule(val) or isinstance(val, str)):
                     raise ValueError("DocTestFinder.find: __test__ values "
                                      "must be strings, functions, methods, "
                                      "classes, or modules: %r" %
@@ -983,7 +984,7 @@
                     val = getattr(obj, valname).__func__
 
                 # Recurse to methods, properties, and nested classes.
-                if ((inspect.isfunction(val) or inspect.isclass(val) or
+                if ((inspect.isroutine(val) or inspect.isclass(val) or
                       isinstance(val, property)) and
                       self._from_module(module, val)):
                     valname = '%s.%s' % (name, valname)
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 2411c9b..6843066 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1592,21 +1592,10 @@
         data = 'The quick Brown fox Jumped over The lazy Dog'.split()
         self.assertRaises(TypeError, sorted, data, None, lambda x,y: 0)
 
-def test_main(verbose=None):
-    test_classes = (BuiltinTest, TestSorted)
-
-    run_unittest(*test_classes)
-
-    # verify reference counting
-    if verbose and hasattr(sys, "gettotalrefcount"):
-        import gc
-        counts = [None] * 5
-        for i in range(len(counts)):
-            run_unittest(*test_classes)
-            gc.collect()
-            counts[i] = sys.gettotalrefcount()
-        print(counts)
-
+def load_tests(loader, tests, pattern):
+    from doctest import DocTestSuite
+    tests.addTest(DocTestSuite(builtins))
+    return tests
 
 if __name__ == "__main__":
-    test_main(verbose=True)
+    unittest.main()
diff --git a/Lib/test/test_doctest.py b/Lib/test/test_doctest.py
index d4ff049..d99a16a 100644
--- a/Lib/test/test_doctest.py
+++ b/Lib/test/test_doctest.py
@@ -644,6 +644,35 @@
     >>> test = doctest.DocTestFinder().find(f)[0]
     >>> [e.lineno for e in test.examples]
     [1, 9, 12]
+
+Finding Doctests in Modules Not Written in Python
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+DocTestFinder can also find doctests in most modules not written in Python.
+We'll use builtins as an example, since it almost certainly isn't written in
+plain ol' Python and is guaranteed to be available.
+
+    >>> import builtins
+    >>> tests = doctest.DocTestFinder().find(builtins)
+    >>> len(tests) # how many objects checked for doctests
+    794
+    >>> real_tests = [t for t in tests if len(t.examples) > 0]
+    >>> len(real_tests) # how many objects actually have doctests
+    8
+    >>> for t in real_tests:
+    ...     print('{}  {}'.format(len(t.examples), t.name))
+    ...
+    1  builtins.bin
+    3  builtins.float.as_integer_ratio
+    2  builtins.float.fromhex
+    2  builtins.float.hex
+    1  builtins.hex
+    1  builtins.int
+    2  builtins.int.bit_length
+    1  builtins.oct
+
+Note here that 'bin', 'oct', and 'hex' are functions; 'float.as_integer_ratio',
+'float.hex', and 'int.bit_length' are methods; 'float.fromhex' is a classmethod,
+and 'int' is a type.
 """
 
 def test_DocTestParser(): r"""
diff --git a/Misc/NEWS b/Misc/NEWS
index ddd9cf6..e24ece8 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -68,6 +68,9 @@
 Library
 -------
 
+- Issue #3158: doctest can now find doctests in functions and methods
+  written in C.
+
 - Issue #13477: Added command line interface to the tarfile module.
   Original patch by Berker Peksag.
 
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index abea975..29c3b32 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -1417,7 +1417,7 @@
 >>> float.fromhex('0x1.ffffp10')\n\
 2047.984375\n\
 >>> float.fromhex('-0x1p-1074')\n\
--4.9406564584124654e-324");
+-5e-324");
 
 
 static PyObject *
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 96ccd64..057ab47 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -350,7 +350,11 @@
 PyDoc_STRVAR(bin_doc,
 "bin(number) -> string\n\
 \n\
-Return the binary representation of an integer.");
+Return the binary representation of an integer.\n\
+\n\
+   >>> bin(2796202)\n\
+   '0b1010101010101010101010'\n\
+");
 
 
 static PyObject *
@@ -1276,7 +1280,11 @@
 PyDoc_STRVAR(hex_doc,
 "hex(number) -> string\n\
 \n\
-Return the hexadecimal representation of an integer.");
+Return the hexadecimal representation of an integer.\n\
+\n\
+   >>> hex(3735928559)\n\
+   '0xdeadbeef'\n\
+");
 
 
 static PyObject *
@@ -1476,7 +1484,11 @@
 PyDoc_STRVAR(oct_doc,
 "oct(number) -> string\n\
 \n\
-Return the octal representation of an integer.");
+Return the octal representation of an integer.\n\
+\n\
+   >>> oct(342391)\n\
+   '0o1234567'\n\
+");
 
 
 static PyObject *