Backport of PEP 3101, Advanced String Formatting, from py3k.

Highlights:
 - Adding PyObject_Format.
 - Adding string.Format class.
 - Adding __format__ for str, unicode, int, long, float, datetime.
 - Adding builtin format.
 - Adding ''.format and u''.format.
 - str/unicode fixups for formatters.

The files in Objects/stringlib that implement PEP 3101 (stringdefs.h,
unicodedefs.h, formatter.h, string_format.h) are identical in trunk
and py3k.  Any changes from here on should be made to trunk, and
changes will propogate to py3k).

Include/abstract.h

@@ -529,6 +529,13 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
 
        */
 
+     PyAPI_FUNC(PyObject *) PyObject_Format(PyObject* obj,
+					    PyObject *format_spec);
+       /*
+	 Takes an arbitrary object and returns the result of
+	 calling obj.__format__(format_spec).
+       */
+
 /* Iterators */
 
      PyAPI_FUNC(PyObject *) PyObject_GetIter(PyObject *);

Include/formatter_string.h

+PyObject *
+string__format__(PyObject *self, PyObject *args);
+
+PyObject *
+string_long__format__(PyObject *self, PyObject *args);
+
+PyObject *
+string_int__format__(PyObject *self, PyObject *args);
+
+PyObject *
+string_float__format__(PyObject *self, PyObject *args);
+

Include/formatter_unicode.h

+PyObject *
+unicode__format__(PyObject *self, PyObject *args);
+
+PyObject *
+unicode_long__format__(PyObject *self, PyObject *args);
+
+PyObject *
+unicode_int__format__(PyObject *self, PyObject *args);
+
+PyObject *
+unicode_float__format__(PyObject *self, PyObject *args);
+

Lib/string.py

@@ -527,3 +527,115 @@ try:
     letters = lowercase + uppercase
 except ImportError:
     pass                                          # Use the original versions
+
+########################################################################
+# the Formatter class
+# see PEP 3101 for details and purpose of this class
+
+# The hard parts are reused from the C implementation.  They're
+# exposed here via the sys module.  sys was chosen because it's always
+# available and doesn't have to be dynamically loaded.
+
+# The overall parser is implemented in str._formatter_parser.
+# The field name parser is implemented in str._formatter_field_name_split
+
+class Formatter(object):
+    def format(self, format_string, *args, **kwargs):
+        return self.vformat(format_string, args, kwargs)
+
+    def vformat(self, format_string, args, kwargs):
+        used_args = set()
+        result = self._vformat(format_string, args, kwargs, used_args, 2)
+        self.check_unused_args(used_args, args, kwargs)
+        return result
+
+    def _vformat(self, format_string, args, kwargs, used_args, recursion_depth):
+        if recursion_depth < 0:
+            raise ValueError('Max string recursion exceeded')
+        result = []
+        for literal_text, field_name, format_spec, conversion in \
+                self.parse(format_string):
+
+            # output the literal text
+            if literal_text:
+                result.append(literal_text)
+
+            # if there's a field, output it
+            if field_name is not None:
+                # this is some markup, find the object and do
+                #  the formatting
+
+                # given the field_name, find the object it references
+                #  and the argument it came from
+                obj, arg_used = self.get_field(field_name, args, kwargs)
+                used_args.add(arg_used)
+
+                # do any conversion on the resulting object
+                obj = self.convert_field(obj, conversion)
+
+                # expand the format spec, if needed
+                format_spec = self._vformat(format_spec, args, kwargs,
+                                            used_args, recursion_depth-1)
+
+                # format the object and append to the result
+                result.append(self.format_field(obj, format_spec))
+
+        return ''.join(result)
+
+
+    def get_value(self, key, args, kwargs):
+        if isinstance(key, (int, long)):
+            return args[key]
+        else:
+            return kwargs[key]
+
+
+    def check_unused_args(self, used_args, args, kwargs):
+        pass
+
+
+    def format_field(self, value, format_spec):
+        return format(value, format_spec)
+
+
+    def convert_field(self, value, conversion):
+        # do any conversion on the resulting object
+        if conversion == 'r':
+            return repr(value)
+        elif conversion == 's':
+            return str(value)
+        elif conversion is None:
+            return value
+        raise ValueError("Unknown converion specifier {0!s}".format(conversion))
+
+
+    # returns an iterable that contains tuples of the form:
+    # (literal_text, field_name, format_spec, conversion)
+    # literal_text can be zero length
+    # field_name can be None, in which case there's no
+    #  object to format and output
+    # if field_name is not None, it is looked up, formatted
+    #  with format_spec and conversion and then used
+    def parse(self, format_string):
+        return format_string._formatter_parser()
+
+
+    # given a field_name, find the object it references.
+    #  field_name:   the field being looked up, e.g. "0.name"
+    #                 or "lookup[3]"
+    #  used_args:    a set of which args have been used
+    #  args, kwargs: as passed in to vformat
+    def get_field(self, field_name, args, kwargs):
+        first, rest = field_name._formatter_field_name_split()
+
+        obj = self.get_value(first, args, kwargs)
+
+        # loop through the rest of the field_name, doing
+        #  getattr or getitem as needed
+        for is_attr, i in rest:
+            if is_attr:
+                obj = getattr(obj, i)
+            else:
+                obj = obj[i]
+
+        return obj, first

Lib/test/test_builtin.py

@@ -2012,6 +2012,101 @@ class TestSorted(unittest.TestCase):
         data = 'The quick Brown fox Jumped over The lazy Dog'.split()
         self.assertRaises(TypeError, sorted, data, None, lambda x,y: 0)
 
+    def test_format(self):
+        # Test the basic machinery of the format() builtin.  Don't test
+        #  the specifics of the various formatters
+        self.assertEqual(format(3, ''), '3')
+
+        # Returns some classes to use for various tests.  There's
+        #  an old-style version, and a new-style version
+        def classes_new():
+            class A(object):
+                def __init__(self, x):
+                    self.x = x
+                def __format__(self, format_spec):
+                    return str(self.x) + format_spec
+            class DerivedFromA(A):
+                pass
+
+            class Simple(object): pass
+            class DerivedFromSimple(Simple):
+                def __init__(self, x):
+                    self.x = x
+                def __format__(self, format_spec):
+                    return str(self.x) + format_spec
+            class DerivedFromSimple2(DerivedFromSimple): pass
+            return A, DerivedFromA, DerivedFromSimple, DerivedFromSimple2
+
+        # In 3.0, classes_classic has the same meaning as classes_new
+        def classes_classic():
+            class A:
+                def __init__(self, x):
+                    self.x = x
+                def __format__(self, format_spec):
+                    return str(self.x) + format_spec
+            class DerivedFromA(A):
+                pass
+
+            class Simple: pass
+            class DerivedFromSimple(Simple):
+                def __init__(self, x):
+                    self.x = x
+                def __format__(self, format_spec):
+                    return str(self.x) + format_spec
+            class DerivedFromSimple2(DerivedFromSimple): pass
+            return A, DerivedFromA, DerivedFromSimple, DerivedFromSimple2
+
+        def class_test(A, DerivedFromA, DerivedFromSimple, DerivedFromSimple2):
+            self.assertEqual(format(A(3), 'spec'), '3spec')
+            self.assertEqual(format(DerivedFromA(4), 'spec'), '4spec')
+            self.assertEqual(format(DerivedFromSimple(5), 'abc'), '5abc')
+            self.assertEqual(format(DerivedFromSimple2(10), 'abcdef'),
+                             '10abcdef')
+
+        class_test(*classes_new())
+        class_test(*classes_classic())
+
+        def empty_format_spec(value):
+            # test that:
+            #  format(x, '') == str(x)
+            #  format(x) == str(x)
+            self.assertEqual(format(value, ""), str(value))
+            self.assertEqual(format(value), str(value))
+
+        # for builtin types, format(x, "") == str(x)
+        empty_format_spec(17**13)
+        empty_format_spec(1.0)
+        empty_format_spec(3.1415e104)
+        empty_format_spec(-3.1415e104)
+        empty_format_spec(3.1415e-104)
+        empty_format_spec(-3.1415e-104)
+        empty_format_spec(object)
+        empty_format_spec(None)
+
+        # TypeError because self.__format__ returns the wrong type
+        class BadFormatResult:
+            def __format__(self, format_spec):
+                return 1.0
+        self.assertRaises(TypeError, format, BadFormatResult(), "")
+
+        # TypeError because format_spec is not unicode or str
+        self.assertRaises(TypeError, format, object(), 4)
+        self.assertRaises(TypeError, format, object(), object())
+
+        # tests for object.__format__ really belong elsewhere, but
+        #  there's no good place to put them
+        x = object().__format__('')
+        self.assert_(x.startswith('<object object at'))
+
+        # first argument to object.__format__ must be string
+        self.assertRaises(TypeError, object().__format__, 3)
+        self.assertRaises(TypeError, object().__format__, object())
+        self.assertRaises(TypeError, object().__format__, None)
+
+        # make sure we can take a subclass of str as a format spec
+        class DerivedFromStr(str): pass
+        self.assertEqual(format(0, DerivedFromStr('10')), '         0')
+
 def test_main(verbose=None):
     test_classes = (BuiltinTest, TestSorted)
 

Lib/test/test_datetime.py

@@ -854,6 +854,32 @@ class TestDate(HarmlessMixedComparison, unittest.TestCase):
         # A naive object replaces %z and %Z w/ empty strings.
         self.assertEqual(t.strftime("'%z' '%Z'"), "'' ''")
 
+    def test_format(self):
+        dt = self.theclass(2007, 9, 10)
+        self.assertEqual(dt.__format__(''), str(dt))
+
+        # check that a derived class's __str__() gets called
+        class A(self.theclass):
+            def __str__(self):
+                return 'A'
+        a = A(2007, 9, 10)
+        self.assertEqual(a.__format__(''), 'A')
+
+        # check that a derived class's strftime gets called
+        class B(self.theclass):
+            def strftime(self, format_spec):
+                return 'B'
+        b = B(2007, 9, 10)
+        self.assertEqual(b.__format__(''), str(dt))
+
+        for fmt in ["m:%m d:%d y:%y",
+                    "m:%m d:%d y:%y H:%H M:%M S:%S",
+                    "%z %Z",
+                    ]:
+            self.assertEqual(dt.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(a.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(b.__format__(fmt), 'B')
+
     def test_resolution_info(self):
         self.assert_(isinstance(self.theclass.min, self.theclass))
         self.assert_(isinstance(self.theclass.max, self.theclass))
@@ -1136,6 +1162,32 @@ class TestDateTime(TestDate):
         # str is ISO format with the separator forced to a blank.
         self.assertEqual(str(t), "0002-03-02 00:00:00")
 
+    def test_format(self):
+        dt = self.theclass(2007, 9, 10, 4, 5, 1, 123)
+        self.assertEqual(dt.__format__(''), str(dt))
+
+        # check that a derived class's __str__() gets called
+        class A(self.theclass):
+            def __str__(self):
+                return 'A'
+        a = A(2007, 9, 10, 4, 5, 1, 123)
+        self.assertEqual(a.__format__(''), 'A')
+
+        # check that a derived class's strftime gets called
+        class B(self.theclass):
+            def strftime(self, format_spec):
+                return 'B'
+        b = B(2007, 9, 10, 4, 5, 1, 123)
+        self.assertEqual(b.__format__(''), str(dt))
+
+        for fmt in ["m:%m d:%d y:%y",
+                    "m:%m d:%d y:%y H:%H M:%M S:%S",
+                    "%z %Z",
+                    ]:
+            self.assertEqual(dt.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(a.__format__(fmt), dt.strftime(fmt))
+            self.assertEqual(b.__format__(fmt), 'B')
+
     def test_more_ctime(self):
         # Test fields that TestDate doesn't touch.
         import time
@@ -1767,6 +1819,30 @@ class TestTime(HarmlessMixedComparison, unittest.TestCase):
         # A naive object replaces %z and %Z with empty strings.
         self.assertEqual(t.strftime("'%z' '%Z'"), "'' ''")
 
+    def test_format(self):
+        t = self.theclass(1, 2, 3, 4)
+        self.assertEqual(t.__format__(''), str(t))
+
+        # check that a derived class's __str__() gets called
+        class A(self.theclass):
+            def __str__(self):
+                return 'A'
+        a = A(1, 2, 3, 4)
+        self.assertEqual(a.__format__(''), 'A')
+
+        # check that a derived class's strftime gets called
+        class B(self.theclass):
+            def strftime(self, format_spec):
+                return 'B'
+        b = B(1, 2, 3, 4)
+        self.assertEqual(b.__format__(''), str(t))
+
+        for fmt in ['%H %M %S',
+                    ]:
+            self.assertEqual(t.__format__(fmt), t.strftime(fmt))
+            self.assertEqual(a.__format__(fmt), t.strftime(fmt))
+            self.assertEqual(b.__format__(fmt), 'B')
+
     def test_str(self):
         self.assertEqual(str(self.theclass(1, 2, 3, 4)), "01:02:03.000004")
         self.assertEqual(str(self.theclass(10, 2, 3, 4000)), "10:02:03.004000")

Lib/test/test_descrtut.py

@@ -183,6 +183,7 @@ Instead, you can get the same information from the list type:
      '__delslice__',
      '__doc__',
      '__eq__',
+     '__format__',
      '__ge__',
      '__getattribute__',
      '__getitem__',

Lib/test/test_string.py

@@ -106,6 +106,92 @@ class ModuleTest(unittest.TestCase):
         self.assertEqual(string.capwords('ABC-DEF-GHI', '-'), 'Abc-Def-Ghi')
         self.assertEqual(string.capwords('ABC-def DEF-ghi GHI'), 'Abc-def Def-ghi Ghi')
 
+    def test_formatter(self):
+        fmt = string.Formatter()
+        self.assertEqual(fmt.format("foo"), "foo")
+
+        self.assertEqual(fmt.format("foo{0}", "bar"), "foobar")
+        self.assertEqual(fmt.format("foo{1}{0}-{1}", "bar", 6), "foo6bar-6")
+        self.assertEqual(fmt.format("-{arg!r}-", arg='test'), "-'test'-")
+
+        # override get_value ############################################
+        class NamespaceFormatter(string.Formatter):
+            def __init__(self, namespace={}):
+                string.Formatter.__init__(self)
+                self.namespace = namespace
+
+            def get_value(self, key, args, kwds):
+                if isinstance(key, str):
+                    try:
+                        # Check explicitly passed arguments first
+                        return kwds[key]
+                    except KeyError:
+                        return self.namespace[key]
+                else:
+                    string.Formatter.get_value(key, args, kwds)
+
+        fmt = NamespaceFormatter({'greeting':'hello'})
+        self.assertEqual(fmt.format("{greeting}, world!"), 'hello, world!')
+
+
+        # override format_field #########################################
+        class CallFormatter(string.Formatter):
+            def format_field(self, value, format_spec):
+                return format(value(), format_spec)
+
+        fmt = CallFormatter()
+        self.assertEqual(fmt.format('*{0}*', lambda : 'result'), '*result*')
+
+
+        # override convert_field ########################################
+        class XFormatter(string.Formatter):
+            def convert_field(self, value, conversion):
+                if conversion == 'x':
+                    return None
+                return super(XFormatter, self).convert_field(value, conversion)
+
+        fmt = XFormatter()
+        self.assertEqual(fmt.format("{0!r}:{0!x}", 'foo', 'foo'), "'foo':None")
+
+
+        # override parse ################################################
+        class BarFormatter(string.Formatter):
+            # returns an iterable that contains tuples of the form:
+            # (literal_text, field_name, format_spec, conversion)
+            def parse(self, format_string):
+                for field in format_string.split('|'):
+                    if field[0] == '+':
+                        # it's markup
+                        field_name, _, format_spec = field[1:].partition(':')
+                        yield '', field_name, format_spec, None
+                    else:
+                        yield field, None, None, None
+
+        fmt = BarFormatter()
+        self.assertEqual(fmt.format('*|+0:^10s|*', 'foo'), '*   foo    *')
+
+        # test all parameters used
+        class CheckAllUsedFormatter(string.Formatter):
+            def check_unused_args(self, used_args, args, kwargs):
+                # Track which arguments actuallly got used
+                unused_args = set(kwargs.keys())
+                unused_args.update(range(0, len(args)))
+
+                for arg in used_args:
+                    unused_args.remove(arg)
+
+                if unused_args:
+                    raise ValueError("unused arguments")
+
+        fmt = CheckAllUsedFormatter()
+        self.assertEqual(fmt.format("{0}", 10), "10")
+        self.assertEqual(fmt.format("{0}{i}", 10, i=100), "10100")
+        self.assertEqual(fmt.format("{0}{i}{1}", 10, 20, i=100), "1010020")
+        self.assertRaises(ValueError, fmt.format, "{0}{i}{1}", 10, 20, i=100, j=0)
+        self.assertRaises(ValueError, fmt.format, "{0}", 10, 20)
+        self.assertRaises(ValueError, fmt.format, "{0}", 10, 20, i=100)
+        self.assertRaises(ValueError, fmt.format, "{i}", 10, 20, i=100)
+
 class BytesAliasTest(unittest.TestCase):
 
     def test_builtin(self):

Lib/test/test_types.py

@@ -266,6 +266,257 @@ class TypesTests(unittest.TestCase):
         except TypeError: pass
         else: self.fail("char buffer (at C level) not working")
 
+    def test_int__format__(self):
+        def test(i, format_spec, result):
+            # just make sure I'm not accidentally checking longs
+            assert type(i) == int
+            assert type(format_spec) == str
+            self.assertEqual(i.__format__(format_spec), result)
+            self.assertEqual(i.__format__(unicode(format_spec)), result)
+
+        test(123456789, 'd', '123456789')
+        test(123456789, 'd', '123456789')
+
+        test(1, 'c', '\01')
+
+        # sign and aligning are interdependent
+        test(1, "-", '1')
+        test(-1, "-", '-1')
+        test(1, "-3", '  1')
+        test(-1, "-3", ' -1')
+        test(1, "+3", ' +1')
+        test(-1, "+3", ' -1')
+        test(1, " 3", '  1')
+        test(-1, " 3", ' -1')
+        test(1, " ", ' 1')
+        test(-1, " ", '-1')
+
+        # hex
+        test(3, "x", "3")
+        test(3, "X", "3")
+        test(1234, "x", "4d2")
+        test(-1234, "x", "-4d2")
+        test(1234, "8x", "     4d2")
+        test(-1234, "8x", "    -4d2")
+        test(1234, "x", "4d2")
+        test(-1234, "x", "-4d2")
+        test(-3, "x", "-3")
+        test(-3, "X", "-3")
+        test(int('be', 16), "x", "be")
+        test(int('be', 16), "X", "BE")
+        test(-int('be', 16), "x", "-be")
+        test(-int('be', 16), "X", "-BE")
+
+        # octal
+        test(3, "o", "3")
+        test(-3, "o", "-3")
+        test(65, "o", "101")
+        test(-65, "o", "-101")
+        test(1234, "o", "2322")
+        test(-1234, "o", "-2322")
+        test(1234, "-o", "2322")
+        test(-1234, "-o", "-2322")
+        test(1234, " o", " 2322")
+        test(-1234, " o", "-2322")
+        test(1234, "+o", "+2322")
+        test(-1234, "+o", "-2322")
+
+        # binary
+        test(3, "b", "11")
+        test(-3, "b", "-11")
+        test(1234, "b", "10011010010")
+        test(-1234, "b", "-10011010010")
+        test(1234, "-b", "10011010010")
+        test(-1234, "-b", "-10011010010")
+        test(1234, " b", " 10011010010")
+        test(-1234, " b", "-10011010010")
+        test(1234, "+b", "+10011010010")
+        test(-1234, "+b", "-10011010010")
+
+        # make sure these are errors
+
+        # precision disallowed
+        self.assertRaises(ValueError, 3 .__format__, "1.3")
+        # sign not allowed with 'c'
+        self.assertRaises(ValueError, 3 .__format__, "+c")
+        # format spec must be string
+        self.assertRaises(TypeError, 3 .__format__, None)
+        self.assertRaises(TypeError, 3 .__format__, 0)
+
+        # ensure that only int and float type specifiers work
+        for format_spec in ([chr(x) for x in range(ord('a'), ord('z')+1)] +
+                            [chr(x) for x in range(ord('A'), ord('Z')+1)]):
+            if not format_spec in 'bcdoxXeEfFgGn%':
+                self.assertRaises(ValueError, 0 .__format__, format_spec)
+                self.assertRaises(ValueError, 1 .__format__, format_spec)
+                self.assertRaises(ValueError, (-1) .__format__, format_spec)
+
+        # ensure that float type specifiers work; format converts
+        #  the int to a float
+        for format_spec in 'eEfFgGn%':
+            for value in [0, 1, -1, 100, -100, 1234567890, -1234567890]:
+                self.assertEqual(value.__format__(format_spec),
+                                 float(value).__format__(format_spec))
+
+    def test_long__format__(self):
+        def test(i, format_spec, result):
+            # make sure we're not accidentally checking ints
+            assert type(i) == long
+            assert type(format_spec) == str
+            self.assertEqual(i.__format__(format_spec), result)
+            self.assertEqual(i.__format__(unicode(format_spec)), result)
+
+        test(10**100, 'd', '1' + '0' * 100)
+        test(10**100+100, 'd', '1' + '0' * 97 + '100')
+
+        test(123456789L, 'd', '123456789')
+        test(123456789L, 'd', '123456789')
+
+        # sign and aligning are interdependent
+        test(1L, "-", '1')
+        test(-1L, "-", '-1')
+        test(1L, "-3", '  1')
+        test(-1L, "-3", ' -1')
+        test(1L, "+3", ' +1')
+        test(-1L, "+3", ' -1')
+        test(1L, " 3", '  1')
+        test(-1L, " 3", ' -1')
+        test(1L, " ", ' 1')
+        test(-1L, " ", '-1')
+
+        test(1L, 'c', '\01')
+
+        # hex
+        test(3L, "x", "3")
+        test(3L, "X", "3")
+        test(1234L, "x", "4d2")
+        test(-1234L, "x", "-4d2")
+        test(1234L, "8x", "     4d2")
+        test(-1234L, "8x", "    -4d2")
+        test(1234L, "x", "4d2")
+        test(-1234L, "x", "-4d2")
+        test(-3L, "x", "-3")
+        test(-3L, "X", "-3")
+        test(long('be', 16), "x", "be")
+        test(long('be', 16), "X", "BE")
+        test(-long('be', 16), "x", "-be")
+        test(-long('be', 16), "X", "-BE")
+
+        # octal
+        test(3L, "o", "3")
+        test(-3L, "o", "-3")
+        test(65L, "o", "101")
+        test(-65L, "o", "-101")
+        test(1234L, "o", "2322")
+        test(-1234L, "o", "-2322")
+        test(1234L, "-o", "2322")
+        test(-1234L, "-o", "-2322")
+        test(1234L, " o", " 2322")
+        test(-1234L, " o", "-2322")
+        test(1234L, "+o", "+2322")
+        test(-1234L, "+o", "-2322")
+
+        # binary
+        test(3L, "b", "11")
+        test(-3L, "b", "-11")
+        test(1234L, "b", "10011010010")
+        test(-1234L, "b", "-10011010010")
+        test(1234L, "-b", "10011010010")
+        test(-1234L, "-b", "-10011010010")
+        test(1234L, " b", " 10011010010")
+        test(-1234L, " b", "-10011010010")
+        test(1234L, "+b", "+10011010010")
+        test(-1234L, "+b", "-10011010010")
+
+        # make sure these are errors
+
+        # precision disallowed
+        self.assertRaises(ValueError, 3L .__format__, "1.3")
+        # sign not allowed with 'c'
+        self.assertRaises(ValueError, 3L .__format__, "+c")
+        # format spec must be string
+        self.assertRaises(TypeError, 3L .__format__, None)
+        self.assertRaises(TypeError, 3L .__format__, 0)
+
+        # ensure that only int and float type specifiers work
+        for format_spec in ([chr(x) for x in range(ord('a'), ord('z')+1)] +
+                            [chr(x) for x in range(ord('A'), ord('Z')+1)]):
+            if not format_spec in 'bcdoxXeEfFgGn%':
+                self.assertRaises(ValueError, 0L .__format__, format_spec)
+                self.assertRaises(ValueError, 1L .__format__, format_spec)
+                self.assertRaises(ValueError, (-1L) .__format__, format_spec)
+
+        # ensure that float type specifiers work; format converts
+        #  the long to a float
+        for format_spec in 'eEfFgGn%':
+            for value in [0L, 1L, -1L, 100L, -100L, 1234567890L, -1234567890L]:
+                self.assertEqual(value.__format__(format_spec),
+                                 float(value).__format__(format_spec))
+
+    def test_float__format__(self):
+        # these should be rewritten to use both format(x, spec) and
+        # x.__format__(spec)
+
+        def test(f, format_spec, result):
+            assert type(f) == float
+            assert type(format_spec) == str
+            self.assertEqual(f.__format__(format_spec), result)
+            self.assertEqual(f.__format__(unicode(format_spec)), result)
+
+        test(0.0, 'f', '0.000000')
+
+        # the default is 'g', except for empty format spec
+        test(0.0, '', '0.0')
+        test(0.01, '', '0.01')
+        test(0.01, 'g', '0.01')
+
+        test( 1.0, ' g', ' 1')
+        test(-1.0, ' g', '-1')
+        test( 1.0, '+g', '+1')
+        test(-1.0, '+g', '-1')
+        test(1.1234e200, 'g', '1.1234e+200')
+        test(1.1234e200, 'G', '1.1234E+200')
+
+
+        test(1.0, 'f', '1.000000')
+
+        test(-1.0, 'f', '-1.000000')
+
+        test( 1.0, ' f', ' 1.000000')
+        test(-1.0, ' f', '-1.000000')
+        test( 1.0, '+f', '+1.000000')
+        test(-1.0, '+f', '-1.000000')
+        test(1.1234e200, 'f', '1.1234e+200')
+        test(1.1234e200, 'F', '1.1234e+200')
+
+        test( 1.0, 'e', '1.000000e+00')
+        test(-1.0, 'e', '-1.000000e+00')
+        test( 1.0, 'E', '1.000000E+00')
+        test(-1.0, 'E', '-1.000000E+00')
+        test(1.1234e20, 'e', '1.123400e+20')
+        test(1.1234e20, 'E', '1.123400E+20')
+
+        # % formatting
+        test(-1.0, '%', '-100.000000%')
+
+        # format spec must be string
+        self.assertRaises(TypeError, 3.0.__format__, None)
+        self.assertRaises(TypeError, 3.0.__format__, 0)
+
+        # other format specifiers shouldn't work on floats,
+        #  in particular int specifiers
+        for format_spec in ([chr(x) for x in range(ord('a'), ord('z')+1)] +
+                            [chr(x) for x in range(ord('A'), ord('Z')+1)]):
+            if not format_spec in 'eEfFgGn%':
+                self.assertRaises(ValueError, format, 0.0, format_spec)
+                self.assertRaises(ValueError, format, 1.0, format_spec)
+                self.assertRaises(ValueError, format, -1.0, format_spec)
+                self.assertRaises(ValueError, format, 1e100, format_spec)
+                self.assertRaises(ValueError, format, -1e100, format_spec)
+                self.assertRaises(ValueError, format, 1e-100, format_spec)
+                self.assertRaises(ValueError, format, -1e-100, format_spec)
+
+
 def test_main():
     run_unittest(TypesTests)
 

Makefile.pre.in

@@ -281,6 +281,8 @@ PYTHON_OBJS=	\
 		Python/getopt.o \
 		Python/pystrcmp.o \
 		Python/pystrtod.o \
+		Python/formatter_unicode.o \
+		Python/formatter_string.o \
 		Python/$(DYNLOADFILE) \
 		$(LIBOBJS) \
 		$(MACHDEP_OBJS) \
@@ -515,6 +517,20 @@ Python/importdl.o: $(srcdir)/Python/importdl.c
 Objects/unicodectype.o:	$(srcdir)/Objects/unicodectype.c \
 				$(srcdir)/Objects/unicodetype_db.h
 
+Objects/unicodeobject.o: $(srcdir)/Objects/unicodeobject.c \
+				$(srcdir)/Objects/stringlib/string_format.h \
+	                        $(srcdir)/Objects/stringlib/unicodedefs.h \
+	                        $(srcdir)/Objects/stringlib/fastsearch.h \
+	                        $(srcdir)/Objects/stringlib/count.h \
+	                        $(srcdir)/Objects/stringlib/find.h \
+	                        $(srcdir)/Objects/stringlib/partition.h
+
+Python/formatter_unicode.o: $(srcdir)/Python/formatter_unicode.c \
+	                        $(srcdir)/Objects/stringlib/formatter.h
+
+Python/formatter_string.o: $(srcdir)/Python/formatter_string.c \
+	                        $(srcdir)/Objects/stringlib/formatter.h
+
 ############################################################################
 # Header files
 

Modules/datetimemodule.c

@@ -2469,6 +2469,32 @@ date_strftime(PyDateTime_Date *self, PyObject *args, PyObject *kw)
 	return result;
 }
 
+static PyObject *
+date_format(PyDateTime_Date *self, PyObject *args)
+{
+	PyObject *format;
+
+	if (!PyArg_ParseTuple(args, "O:__format__", &format))
+		return NULL;
+
+	/* Check for str or unicode */
+	if (PyString_Check(format)) {
+                /* If format is zero length, return str(self) */
+		if (PyString_GET_SIZE(format) == 0)
+			return PyObject_Str((PyObject *)self);
+	} else if (PyUnicode_Check(format)) {
+                /* If format is zero length, return str(self) */
+		if (PyUnicode_GET_SIZE(format) == 0)
+			return PyObject_Unicode((PyObject *)self);
+	} else {
+		PyErr_Format(PyExc_ValueError,
+			     "__format__ expects str or unicode, not %.200s",
+			     Py_TYPE(format)->tp_name);
+		return NULL;
+	}
+	return PyObject_CallMethod((PyObject *)self, "strftime", "O", format);
+}
+
 /* ISO methods. */
 
 static PyObject *
@@ -2633,6 +2659,9 @@ static PyMethodDef date_methods[] = {
 	{"strftime",   	(PyCFunction)date_strftime,	METH_VARARGS | METH_KEYWORDS,
 	 PyDoc_STR("format -> strftime() style string.")},
 
+	{"__format__", 	(PyCFunction)date_format,	METH_VARARGS,
+	 PyDoc_STR("Formats self with strftime.")},
+
 	{"timetuple",   (PyCFunction)date_timetuple,    METH_NOARGS,
          PyDoc_STR("Return time tuple, compatible with time.localtime().")},
 
@@ -3418,6 +3447,9 @@ static PyMethodDef time_methods[] = {
 	{"strftime",   	(PyCFunction)time_strftime,	METH_VARARGS | METH_KEYWORDS,
 	 PyDoc_STR("format -> strftime() style string.")},
 
+	{"__format__", 	(PyCFunction)date_format,	METH_VARARGS,
+	 PyDoc_STR("Formats self with strftime.")},
+
 	{"utcoffset",	(PyCFunction)time_utcoffset,	METH_NOARGS,
 	 PyDoc_STR("Return self.tzinfo.utcoffset(self).")},
 

Objects/abstract.c

@@ -348,6 +348,138 @@ int PyObject_AsWriteBuffer(PyObject *obj,
 	return 0;
 }
 
+PyObject *
+PyObject_Format(PyObject* obj, PyObject *format_spec)
+{
+	static PyObject * str__format__ = NULL;
+	PyObject *empty = NULL;
+	PyObject *result = NULL;
+	int spec_is_unicode;
+	int result_is_unicode;
+
+	/* Initialize cached value */
+	if (str__format__ == NULL) {
+		/* Initialize static variable needed by _PyType_Lookup */
+		str__format__ = PyString_InternFromString("__format__");
+		if (str__format__ == NULL)
+			goto done;
+	}
+
+	/* If no format_spec is provided, use an empty string */
+	if (format_spec == NULL) {
+		empty = PyString_FromStringAndSize(NULL, 0);
+		format_spec = empty;
+	}
+
+	/* Check the format_spec type, and make sure it's str or unicode */
+	if (PyUnicode_Check(format_spec))
+		spec_is_unicode = 1;
+	else if (PyString_Check(format_spec))
+		spec_is_unicode = 0;
+	else {
+		PyErr_Format(PyExc_TypeError,
+			     "format expects arg 2 to be string "
+			     "or unicode, not %.100s", Py_TYPE(format_spec)->tp_name);
+		goto done;
+	}
+
+	/* Make sure the type is initialized.  float gets initialized late */
+	if (Py_TYPE(obj)->tp_dict == NULL)
+		if (PyType_Ready(Py_TYPE(obj)) < 0)
+			goto done;
+
+	/* Check for a __format__ method and call it. */
+	if (PyInstance_Check(obj)) {
+		/* We're an instance of a classic class */
+		PyObject *bound_method = PyObject_GetAttr(obj,
+							  str__format__);
+		if (bound_method != NULL) {
+			result = PyObject_CallFunctionObjArgs(bound_method,
+							      format_spec,
+							      NULL);
+			Py_DECREF(bound_method);
+		} else {
+			PyObject *self_as_str;
+			PyObject *format_method;
+
+			PyErr_Clear();
+			/* Per the PEP, convert to str (or unicode,
+			   depending on the type of the format
+			   specifier).  For new-style classes, this
+			   logic is done by object.__format__(). */
+			if (spec_is_unicode)
+				self_as_str = PyObject_Unicode(obj);
+			else
+				self_as_str = PyObject_Str(obj);
+			if (self_as_str == NULL)
+				goto done;
+
+			/* Then call str.__format__ on that result */
+			format_method = PyObject_GetAttr(self_as_str,
+							 str__format__);
+			if (format_method == NULL) {
+				Py_DECREF(self_as_str);
+				goto done;
+			}
+                        result = PyObject_CallFunctionObjArgs(format_method,
+							      format_spec,
+							      NULL);
+			Py_DECREF(self_as_str);
+			Py_DECREF(format_method);
+			if (result == NULL)
+				goto done;
+                }
+	} else {
+		/* Not an instance of a classic class, use the code
+		   from py3k */
+
+		/* Find the (unbound!) __format__ method (a borrowed
+		   reference) */
+		PyObject *method = _PyType_Lookup(Py_TYPE(obj),
+						  str__format__);
+		if (method == NULL) {
+			PyErr_Format(PyExc_TypeError,
+				     "Type %.100s doesn't define __format__",
+				     Py_TYPE(obj)->tp_name);
+			goto done;
+		}
+		/* And call it, binding it to the value */
+		result = PyObject_CallFunctionObjArgs(method, obj,
+						      format_spec, NULL);
+	}
+
+	if (result == NULL)
+		goto done;
+
+	/* Check the result type, and make sure it's str or unicode */
+	if (PyUnicode_Check(result))
+		result_is_unicode = 1;
+	else if (PyString_Check(result))
+		result_is_unicode = 0;
+	else {
+		PyErr_Format(PyExc_TypeError,
+			     "%.100s.__format__ must return string or "
+			     "unicode, not %.100s", Py_TYPE(obj)->tp_name,
+			     Py_TYPE(result)->tp_name);
+		Py_DECREF(result);
+		result = NULL;
+		goto done;
+	}
+
+	/* Convert to unicode, if needed.  Required if spec is unicode
+	   and result is str */
+	if (spec_is_unicode && !result_is_unicode) {
+		PyObject *tmp = PyObject_Unicode(result);
+		/* This logic works whether or not tmp is NULL */
+		Py_DECREF(result);
+		result = tmp;
+	}
+
+done:
+	Py_XDECREF(empty);
+	return result;
+}
+
 /* Operations on numbers */
 
 int

Objects/floatobject.c

@@ -10,6 +10,7 @@
 #include <ctype.h>
 #include <float.h>
 
+#include "formatter_string.h"
 
 #if !defined(__STDC__)
 extern double fmod(double, double);
@@ -1434,6 +1435,46 @@ float_getzero(PyObject *v, void *closure)
 	return PyFloat_FromDouble(0.0);
 }
 
+static PyObject *
+float__format__(PyObject *self, PyObject *args)
+{
+	PyObject *format_spec;
+
+	if (!PyArg_ParseTuple(args, "O:__format__", &format_spec))
+		return NULL;
+	if (PyString_Check(format_spec))
+		return string_float__format__(self, args);
+	if (PyUnicode_Check(format_spec)) {
+		/* Convert format_spec to a str */
+		PyObject *result = NULL;
+		PyObject *newargs = NULL;
+		PyObject *string_format_spec = NULL;
+
+		string_format_spec = PyObject_Str(format_spec);
+		if (string_format_spec == NULL)
+			goto done;
+
+		newargs = Py_BuildValue("(O)", string_format_spec);
+		if (newargs == NULL)
+			goto done;
+
+		result = string_float__format__(self, newargs);
+
+		done:
+		Py_XDECREF(string_format_spec);
+		Py_XDECREF(newargs);
+		return result;
+	}
+	PyErr_SetString(PyExc_TypeError, "__format__ requires str or unicode");
+	return NULL;
+}
+
+PyDoc_STRVAR(float__format__doc,
+"float.__format__(format_spec) -> string\n"
+"\n"
+"Formats the float according to format_spec.");
+
+
 static PyMethodDef float_methods[] = {
   	{"conjugate",	(PyCFunction)float_float,	METH_NOARGS,
 	 "Returns self, the complex conjugate of any float."},
@@ -1446,6 +1487,8 @@ static PyMethodDef float_methods[] = {
 	 METH_O|METH_CLASS,		float_getformat_doc},
 	{"__setformat__",	(PyCFunction)float_setformat,	
 	 METH_VARARGS|METH_CLASS,	float_setformat_doc},
+        {"__format__",          (PyCFunction)float__format__,
+         METH_VARARGS,                  float__format__doc},
 	{NULL,		NULL}		/* sentinel */
 };
 

Objects/intobject.c

@@ -3,6 +3,7 @@
 
 #include "Python.h"
 #include <ctype.h>
+#include "formatter_string.h"
 
 static PyObject *int_int(PyIntObject *v);
 
@@ -1108,12 +1109,47 @@ _PyInt_Format(PyIntObject *v, int base, int newstyle)
 	return PyString_FromStringAndSize(p, &buf[sizeof(buf)] - p);
 }
 
+static PyObject *
+int__format__(PyObject *self, PyObject *args)
+{
+	PyObject *format_spec;
+
+	if (!PyArg_ParseTuple(args, "O:__format__", &format_spec))
+		return NULL;
+	if (PyString_Check(format_spec))
+		return string_int__format__(self, args);
+	if (PyUnicode_Check(format_spec)) {
+		/* Convert format_spec to a str */
+		PyObject *result = NULL;
+		PyObject *newargs = NULL;
+		PyObject *string_format_spec = NULL;
+
+		string_format_spec = PyObject_Str(format_spec);
+		if (string_format_spec == NULL)
+			goto done;
+
+		newargs = Py_BuildValue("(O)", string_format_spec);
+		if (newargs == NULL)
+			goto done;
+
+		result = string_int__format__(self, newargs);
+
+		done:
+		Py_XDECREF(string_format_spec);
+		Py_XDECREF(newargs);
+		return result;
+	}
+	PyErr_SetString(PyExc_TypeError, "__format__ requires str or unicode");
+	return NULL;
+}
+
 static PyMethodDef int_methods[] = {
 	{"conjugate",	(PyCFunction)int_int,	METH_NOARGS,
 	 "Returns self, the complex conjugate of any int."},
 	{"__trunc__",	(PyCFunction)int_int,	METH_NOARGS,
          "Truncating an Integral returns itself."},
 	{"__getnewargs__",	(PyCFunction)int_getnewargs,	METH_NOARGS},
+        {"__format__", (PyCFunction)int__format__, METH_VARARGS},
 	{NULL,		NULL}		/* sentinel */
 };
 

Objects/longobject.c

@@ -6,6 +6,7 @@
 
 #include "Python.h"
 #include "longintrepr.h"
+#include "formatter_string.h"
 
 #include <ctype.h>
 
@@ -3380,12 +3381,47 @@ long_getN(PyLongObject *v, void *context) {
 	return PyLong_FromLong((intptr_t)context);
 }
 
+static PyObject *
+long__format__(PyObject *self, PyObject *args)
+{
+	PyObject *format_spec;
+
+	if (!PyArg_ParseTuple(args, "O:__format__", &format_spec))
+		return NULL;
+	if (PyString_Check(format_spec))
+		return string_long__format__(self, args);
+	if (PyUnicode_Check(format_spec)) {
+		/* Convert format_spec to a str */
+		PyObject *result = NULL;
+		PyObject *newargs = NULL;
+		PyObject *string_format_spec = NULL;
+
+		string_format_spec = PyObject_Str(format_spec);
+		if (string_format_spec == NULL)
+			goto done;
+
+		newargs = Py_BuildValue("(O)", string_format_spec);
+		if (newargs == NULL)
+			goto done;
+
+		result = string_long__format__(self, newargs);
+
+		done:
+		Py_XDECREF(string_format_spec);
+		Py_XDECREF(newargs);
+		return result;
+	}
+	PyErr_SetString(PyExc_TypeError, "__format__ requires str or unicode");
+	return NULL;
+}
+
 static PyMethodDef long_methods[] = {
 	{"conjugate",	(PyCFunction)long_long,	METH_NOARGS,
 	 "Returns self, the complex conjugate of any long."},
 	{"__trunc__",	(PyCFunction)long_long,	METH_NOARGS,
          "Truncating an Integral returns itself."},
 	{"__getnewargs__",	(PyCFunction)long_getnewargs,	METH_NOARGS},
+        {"__format__", (PyCFunction)long__format__, METH_VARARGS},
 	{NULL,		NULL}		/* sentinel */
 };
 

Objects/stringlib/stringdefs.h

+#ifndef STRINGLIB_STRINGDEFS_H
+#define STRINGLIB_STRINGDEFS_H
+
+/* this is sort of a hack.  there's at least one place (formatting
+   floats) where some stringlib code takes a different path if it's
+   compiled as unicode. */
+#define STRINGLIB_IS_UNICODE     0
+
+#define STRINGLIB_OBJECT         PyStringObject
+#define STRINGLIB_CHAR           char
+#define STRINGLIB_TYPE_NAME      "string"
+#define STRINGLIB_PARSE_CODE     "S"
+#define STRINGLIB_EMPTY          nullstring
+#define STRINGLIB_ISDECIMAL(x)   ((x >= '0') && (x <= '9'))
+#define STRINGLIB_TODECIMAL(x)   (STRINGLIB_ISDECIMAL(x) ? (x - '0') : -1)
+#define STRINGLIB_TOUPPER        toupper
+#define STRINGLIB_TOLOWER        tolower
+#define STRINGLIB_FILL           memset
+#define STRINGLIB_STR            PyString_AS_STRING
+#define STRINGLIB_LEN            PyString_GET_SIZE
+#define STRINGLIB_NEW            PyString_FromStringAndSize
+#define STRINGLIB_RESIZE         _PyString_Resize
+#define STRINGLIB_CHECK          PyString_Check
+#define STRINGLIB_CMP            memcmp
+#define STRINGLIB_TOSTR          PyObject_Str
+
+#endif /* !STRINGLIB_STRINGDEFS_H */

Objects/stringlib/unicodedefs.h

+#ifndef STRINGLIB_UNICODEDEFS_H
+#define STRINGLIB_UNICODEDEFS_H
+
+/* this is sort of a hack.  there's at least one place (formatting
+   floats) where some stringlib code takes a different path if it's
+   compiled as unicode. */
+#define STRINGLIB_IS_UNICODE     1
+
+#define STRINGLIB_OBJECT         PyUnicodeObject
+#define STRINGLIB_CHAR           Py_UNICODE
+#define STRINGLIB_TYPE_NAME      "unicode"
+#define STRINGLIB_PARSE_CODE     "U"
+#define STRINGLIB_EMPTY          unicode_empty
+#define STRINGLIB_ISDECIMAL      Py_UNICODE_ISDECIMAL
+#define STRINGLIB_TODECIMAL      Py_UNICODE_TODECIMAL
+#define STRINGLIB_TOUPPER        Py_UNICODE_TOUPPER
+#define STRINGLIB_TOLOWER        Py_UNICODE_TOLOWER
+#define STRINGLIB_FILL           Py_UNICODE_FILL
+#define STRINGLIB_STR            PyUnicode_AS_UNICODE
+#define STRINGLIB_LEN            PyUnicode_GET_SIZE
+#define STRINGLIB_NEW            PyUnicode_FromUnicode
+#define STRINGLIB_RESIZE         PyUnicode_Resize
+#define STRINGLIB_CHECK          PyUnicode_Check
+
+#if PY_VERSION_HEX < 0x03000000
+#define STRINGLIB_TOSTR          PyObject_Unicode
+#else
+#define STRINGLIB_TOSTR          PyObject_Str
+#endif
+
+#define STRINGLIB_WANT_CONTAINS_OBJ 1
+
+/* STRINGLIB_CMP was defined as:
+
+Py_LOCAL_INLINE(int)
+STRINGLIB_CMP(const Py_UNICODE* str, const Py_UNICODE* other, Py_ssize_t len)
+{
+    if (str[0] != other[0])
+        return 1;
+    return memcmp((void*) str, (void*) other, len * sizeof(Py_UNICODE));
+}
+
+but unfortunately that gives a error if the function isn't used in a file that
+includes this file.  So, reluctantly convert it to a macro instead. */
+
+#define STRINGLIB_CMP(str, other, len) \
+    (((str)[0] != (other)[0]) ? \
+     1 : \
+     memcmp((void*) (str), (void*) (other), (len) * sizeof(Py_UNICODE)))
+
+
+#endif /* !STRINGLIB_UNICODEDEFS_H */

Objects/stringobject.c

@@ -4,6 +4,8 @@
 
 #include "Python.h"
 
+#include "formatter_string.h"
+
 #include <ctype.h>
 
 #ifdef COUNT_ALLOCS
@@ -771,15 +773,7 @@ PyString_AsStringAndSize(register PyObject *obj,
 /* -------------------------------------------------------------------- */
 /* Methods */
 
-#define STRINGLIB_CHAR char
-
-#define STRINGLIB_CMP memcmp
-#define STRINGLIB_LEN PyString_GET_SIZE
-#define STRINGLIB_NEW PyString_FromStringAndSize
-#define STRINGLIB_STR PyString_AS_STRING
-
-#define STRINGLIB_EMPTY nullstring
-
+#include "stringlib/stringdefs.h"
 #include "stringlib/fastsearch.h"
 
 #include "stringlib/count.h"
@@ -3910,6 +3904,19 @@ string_getnewargs(PyStringObject *v)
 	return Py_BuildValue("(s#)", v->ob_sval, Py_SIZE(v));
 }
 
+
+#include "stringlib/string_format.h"
+
+PyDoc_STRVAR(format__doc__,
+"S.format(*args, **kwargs) -> unicode\n\
+\n\
+");
+
+PyDoc_STRVAR(p_format__doc__,
+"S.__format__(format_spec) -> unicode\n\
+\n\
+");
+
 
 static PyMethodDef
 string_methods[] = {
@@ -3954,6 +3961,10 @@ string_methods[] = {
 	{"rjust", (PyCFunction)string_rjust, METH_VARARGS, rjust__doc__},
 	{"center", (PyCFunction)string_center, METH_VARARGS, center__doc__},
 	{"zfill", (PyCFunction)string_zfill, METH_VARARGS, zfill__doc__},
+	{"format", (PyCFunction) do_string_format, METH_VARARGS | METH_KEYWORDS, format__doc__},
+	{"__format__", (PyCFunction) string__format__, METH_VARARGS, p_format__doc__},
+	{"_formatter_field_name_split", (PyCFunction) formatter_field_name_split, METH_NOARGS},
+	{"_formatter_parser", (PyCFunction) formatter_parser, METH_NOARGS},
 	{"encode", (PyCFunction)string_encode, METH_VARARGS, encode__doc__},
 	{"decode", (PyCFunction)string_decode, METH_VARARGS, decode__doc__},
 	{"expandtabs", (PyCFunction)string_expandtabs, METH_VARARGS,

Objects/typeobject.c

@@ -3210,11 +3210,57 @@ object_reduce_ex(PyObject *self, PyObject *args)
 	return _common_reduce(self, proto);
 }
 
+/*
+   from PEP 3101, this code implements:
+
+   class object:
+       def __format__(self, format_spec):
+           if isinstance(format_spec, str):
+               return format(str(self), format_spec)
+           elif isinstance(format_spec, unicode):
+               return format(unicode(self), format_spec)
+*/
+static PyObject *
+object_format(PyObject *self, PyObject *args)
+{
+        PyObject *format_spec;
+        PyObject *self_as_str = NULL;
+        PyObject *result = NULL;
+        PyObject *format_meth = NULL;
+
+        if (!PyArg_ParseTuple(args, "O:__format__", &format_spec))
+                return NULL;
+	if (PyUnicode_Check(format_spec)) {
+	        self_as_str = PyObject_Unicode(self);
+	} else if (PyString_Check(format_spec)) {
+	        self_as_str = PyObject_Str(self);
+	} else {
+	        PyErr_SetString(PyExc_TypeError, "argument to __format__ must be unicode or str");
+	        return NULL;
+	}
+
+        if (self_as_str != NULL) {
+                /* find the format function */
+                format_meth = PyObject_GetAttrString(self_as_str, "__format__");
+                if (format_meth != NULL) {
+                       /* and call it */
+                        result = PyObject_CallFunctionObjArgs(format_meth, format_spec, NULL);
+                }
+        }
+
+        Py_XDECREF(self_as_str);
+        Py_XDECREF(format_meth);
+
+        return result;
+}
+
 static PyMethodDef object_methods[] = {
 	{"__reduce_ex__", object_reduce_ex, METH_VARARGS,
 	 PyDoc_STR("helper for pickle")},
 	{"__reduce__", object_reduce, METH_VARARGS,
 	 PyDoc_STR("helper for pickle")},
+        {"__format__", object_format, METH_VARARGS,
+         PyDoc_STR("default object formatter")},
 	{0}
 };
 

Objects/unicodeobject.c

@@ -42,6 +42,8 @@ OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
 
+#include "formatter_unicode.h"
+
 #include "unicodeobject.h"
 #include "ucnhash.h"
 
@@ -5059,21 +5061,8 @@ int PyUnicode_EncodeDecimal(Py_UNICODE *s,
 
 /* --- Helpers ------------------------------------------------------------ */
 
-#define STRINGLIB_CHAR Py_UNICODE
-
-#define STRINGLIB_LEN PyUnicode_GET_SIZE
-#define STRINGLIB_NEW PyUnicode_FromUnicode
-#define STRINGLIB_STR PyUnicode_AS_UNICODE
-
-Py_LOCAL_INLINE(int)
-STRINGLIB_CMP(const Py_UNICODE* str, const Py_UNICODE* other, Py_ssize_t len)
-{
-    if (str[0] != other[0])
-        return 1;
-    return memcmp((void*) str, (void*) other, len * sizeof(Py_UNICODE));
-}
+#include "stringlib/unicodedefs.h"
 
-#define STRINGLIB_EMPTY unicode_empty
 #define FROM_UNICODE
 
 #include "stringlib/fastsearch.h"
@@ -7802,6 +7791,19 @@ unicode_endswith(PyUnicodeObject *self,
 }
 
 
+/* Implements do_string_format, which is unicode because of stringlib */
+#include "stringlib/string_format.h"
+
+PyDoc_STRVAR(format__doc__,
+"S.format(*args, **kwargs) -> unicode\n\
+\n\
+");
+
+PyDoc_STRVAR(p_format__doc__,
+"S.__format__(format_spec) -> unicode\n\
+\n\
+");
+
 
 static PyObject *
 unicode_getnewargs(PyUnicodeObject *v)
@@ -7855,6 +7857,10 @@ static PyMethodDef unicode_methods[] = {
     {"isalpha", (PyCFunction) unicode_isalpha, METH_NOARGS, isalpha__doc__},
     {"isalnum", (PyCFunction) unicode_isalnum, METH_NOARGS, isalnum__doc__},
     {"zfill", (PyCFunction) unicode_zfill, METH_VARARGS, zfill__doc__},
+    {"format", (PyCFunction) do_string_format, METH_VARARGS | METH_KEYWORDS, format__doc__},
+    {"__format__", (PyCFunction) unicode__format__, METH_VARARGS, p_format__doc__},
+    {"_formatter_field_name_split", (PyCFunction) formatter_field_name_split, METH_NOARGS},
+    {"_formatter_parser", (PyCFunction) formatter_parser, METH_NOARGS},
 #if 0
     {"capwords", (PyCFunction) unicode_capwords, METH_NOARGS, capwords__doc__},
 #endif

Python/bltinmodule.c

@@ -338,6 +338,24 @@ PyDoc_STRVAR(filter_doc,
 "function is None, return the items that are true.  If sequence is a tuple\n"
 "or string, return the same type, else return a list.");
 
+static PyObject *
+builtin_format(PyObject *self, PyObject *args)
+{
+	PyObject *value;
+	PyObject *format_spec = NULL;
+
+	if (!PyArg_ParseTuple(args, "O|O:format", &value, &format_spec))
+		return NULL;
+
+	return PyObject_Format(value, format_spec);
+}
+
+PyDoc_STRVAR(format_doc,
+"format(value[, format_spec]) -> string\n\
+\n\
+Returns value.__format__(format_spec)\n\
+format_spec defaults to \"\"");
+
 static PyObject *
 builtin_chr(PyObject *self, PyObject *args)
 {
@@ -2359,6 +2377,7 @@ static PyMethodDef builtin_methods[] = {
  	{"eval",	builtin_eval,       METH_VARARGS, eval_doc},
  	{"execfile",	builtin_execfile,   METH_VARARGS, execfile_doc},
  	{"filter",	builtin_filter,     METH_VARARGS, filter_doc},
+ 	{"format",	builtin_format,     METH_VARARGS, format_doc},
  	{"getattr",	builtin_getattr,    METH_VARARGS, getattr_doc},
  	{"globals",	(PyCFunction)builtin_globals,    METH_NOARGS, globals_doc},
  	{"hasattr",	builtin_hasattr,    METH_VARARGS, hasattr_doc},

Python/formatter_string.c

+/***********************************************************************/
+/* Implements the string (as opposed to unicode) version of the
+   built-in formatters for string, int, float.  That is, the versions
+   of int.__float__, etc., that take and return string objects */
+
+#include "Python.h"
+#include "formatter_string.h"
+
+#include "../Objects/stringlib/stringdefs.h"
+
+#define FORMAT_STRING string__format__
+#define FORMAT_LONG   string_long__format__
+#define FORMAT_INT    string_int__format__
+#define FORMAT_FLOAT  string_float__format__
+#include "../Objects/stringlib/formatter.h"

Python/formatter_unicode.c

+/* Implements the unicode (as opposed to string) version of the
+   built-in formatter for unicode.  That is, unicode.__format__(). */
+
+#include "Python.h"
+#include "formatter_unicode.h"
+
+#include "../Objects/stringlib/unicodedefs.h"
+
+#define FORMAT_STRING unicode__format__
+/* don't define FORMAT_LONG and FORMAT_FLOAT, since we can live
+   with only the string versions of those.  The builtin format()
+   will convert them to unicode. */
+#include "../Objects/stringlib/formatter.h"