Added __format__ method to datetime.datetime, datetime.date, and datetime.time.

If format_spec is empty, __format__ calls str(self), else it calls
self.strftime(format_spec).

Lib/test/test_datetime.py

@@ -849,6 +849,32 @@ 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(format(dt, ''), 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(format(a, ''), '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(format(b, ''), 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(format(dt, fmt), dt.strftime(fmt))
+            self.assertEqual(format(a, fmt), dt.strftime(fmt))
+            self.assertEqual(format(b, fmt), 'B')
+
     def test_resolution_info(self):
         self.assert_(isinstance(self.theclass.min, self.theclass))
         self.assert_(isinstance(self.theclass.max, self.theclass))
@@ -1150,6 +1176,34 @@ 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(format(dt, ''), 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(format(a, ''), '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(format(b, ''), 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(format(dt, fmt), dt.strftime(fmt))
+            self.assertEqual(format(a, fmt), dt.strftime(fmt))
+            self.assertEqual(format(b, fmt), 'B')
+
+
+
     def test_more_ctime(self):
         # Test fields that TestDate doesn't touch.
         import time
@@ -1781,6 +1835,30 @@ 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(format(t, ''), 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(format(a, ''), '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(format(b, ''), str(t))
+
+        for fmt in ['%H %M %S',
+                    ]:
+            self.assertEqual(format(t, fmt), t.strftime(fmt))
+            self.assertEqual(format(a, fmt), t.strftime(fmt))
+            self.assertEqual(format(b, 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")

Modules/datetimemodule.c

@@ -2440,6 +2440,21 @@ 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, "U:__format__", &format))
+		return NULL;
+
+	/* if the format is zero length, return str(self) */
+	if (PyUnicode_GetSize(format) == 0)
+                return PyObject_Unicode((PyObject *)self);
+
+        return PyObject_CallMethod((PyObject *)self, "strftime", "O", format);
+}
+
 /* ISO methods. */
 
 static PyObject *
@@ -2610,6 +2625,9 @@ 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().")},
 
@@ -3198,6 +3216,21 @@ time_strftime(PyDateTime_Time *self, PyObject *args, PyObject *kw)
 	return result;
 }
 
+static PyObject *
+time_format(PyDateTime_Time *self, PyObject *args)
+{
+	PyObject *format;
+
+	if (!PyArg_ParseTuple(args, "U:__format__", &format))
+		return NULL;
+
+	/* if the format is zero length, return str(self) */
+	if (PyUnicode_GetSize(format) == 0)
+                return PyObject_Unicode((PyObject *)self);
+
+        return PyObject_CallMethod((PyObject *)self, "strftime", "O", format);
+}
+
 /*
  * Miscellaneous methods.
  */
@@ -3385,6 +3418,9 @@ static PyMethodDef time_methods[] = {
 	{"strftime",   	(PyCFunction)time_strftime,	METH_VARARGS | METH_KEYWORDS,
 	 PyDoc_STR("format -> strftime() style string.")},
 
+	{"__format__", 	(PyCFunction)time_format,	METH_VARARGS,
+	 PyDoc_STR("Formats self with strftime.")},
+
 	{"utcoffset",	(PyCFunction)time_utcoffset,	METH_NOARGS,
 	 PyDoc_STR("Return self.tzinfo.utcoffset(self).")},