diff -r bcb02458ef78 Doc/library/calendar.rst
--- a/Doc/library/calendar.rst	Tue Sep 21 01:02:10 2010 +0200
+++ b/Doc/library/calendar.rst	Mon Sep 20 23:26:49 2010 -0400
@@ -201,6 +201,13 @@
    Returns the current setting for the weekday to start each week.
 
 
+.. function:: dayofyear(year, month, day)
+
+   Returns the integer between 1 and 366 (inclusive) representing the specified
+   *day* (``1``--``31``) in the specified *month* (``1``--``12``) of the
+   specified *year*.
+
+
 .. function:: isleap(year)
 
    Returns :const:`True` if *year* is a leap year, otherwise :const:`False`.
diff -r bcb02458ef78 Lib/calendar.py
--- a/Lib/calendar.py	Tue Sep 21 01:02:10 2010 +0200
+++ b/Lib/calendar.py	Mon Sep 20 23:26:49 2010 -0400
@@ -113,6 +113,17 @@
     return datetime.date(year, month, day).weekday()
 
 
+def dayofyear(year, month, day):
+    """Returns the integer between 1 and 366 (inclusive) representing the
+    specified day in the specified month of the specified year.
+
+    """
+    # Get the ordinal of the desired day and of the first day of that year.
+    desired_day = datetime.date(year, month, day).toordinal()
+    first_day_of_year = datetime.date(year, 1, 1).toordinal()
+    return desired_day - first_day_of_year + 1
+
+
 def monthrange(year, month):
     """Return weekday (0-6 ~ Mon-Sun) and number of days (28-31) for
        year, month."""
diff -r bcb02458ef78 Lib/test/test_calendar.py
--- a/Lib/test/test_calendar.py	Tue Sep 21 01:02:10 2010 +0200
+++ b/Lib/test/test_calendar.py	Mon Sep 20 23:26:49 2010 -0400
@@ -250,6 +250,22 @@
             # verify it "acts like a sequence" in two forms of iteration
             self.assertEqual(value[::-1], list(reversed(value)))
 
+    def test_dayofyear(self):
+        """Test for the calendar.dayofyear() function, which computes the
+        integer between 1 and 366 (inclusive) representing the specified day in
+        the specified month of the specified year.
+
+        """
+        expected_day_of_year = 1
+        for month in range(1, 13):
+            for day in range(1, calendar.mdays[month] + 1):
+                day_of_year = calendar.dayofyear(2010, month, day)
+                self.assertEqual(expected_day_of_year, day_of_year)
+                # The computed day of the year must be between 1 and 366.
+                self.assertGreaterEqual(day_of_year, 1)
+                self.assertLessEqual(day_of_year, 366)
+                expected_day_of_year += 1
+
 
 class MonthCalendarTestCase(unittest.TestCase):
     def setUp(self):