Starts for each quarter

backdrop/core/timeseries.py

@@ -89,9 +89,13 @@ class Quarter(Period):
     def __init__(self):
         self.name = "month"
         self._delta = relativedelta(months=3)
+        self.quarter_starts = [10, 7, 4, 1]
 
     def start(self, timestamp):
-        return timestamp.replace(month=10, day=1, hour=0, minute=0,
+        quarter_month = next(quarter for quarter in self.quarter_starts
+                             if timestamp.month >= quarter)
+
+        return timestamp.replace(month=quarter_month, day=1, hour=0, minute=0,
                                  second=0, microsecond=0)
 
     def valid_start_at(self, timestamp):

tests/core/test_timeseries.py

@@ -293,9 +293,22 @@ def test_that_a_range_of_five_hours_gives_us_five_data_points(self):
         ))
 
 class TestQuarter(TestCase):
-    def test_that_returns_the_beginning_of_the_current_quarter(self):
-        some_datetime = d(2013, 12, 4, 10, 23, 43)
+    def test_that_returns_the_beginning_of_the_first_quarter(self):
+        some_datetime = d(2013, 1, 20, 0, 23, 43)
+
+        assert_that(QUARTER.start(some_datetime), is_(d(2013, 1, 1, 0, 0, 0)))
+
+    def test_that_returns_the_beginning_of_the_second_quarter(self):
+        some_datetime = d(2013, 5, 20, 0, 23, 43)
+
+        assert_that(QUARTER.start(some_datetime), is_(d(2013, 4, 1, 0, 0, 0)))
 
-        start = QUARTER.start(some_datetime)
+    def test_that_returns_the_beginning_of_the_third_quarter(self):
+        some_datetime = d(2013, 9, 20, 0, 23, 43)
+
+        assert_that(QUARTER.start(some_datetime), is_(d(2013, 7, 1, 0, 0, 0)))
+
+    def test_that_returns_the_beginning_of_the_fourth_quarter(self):
+        some_datetime = d(2013, 12, 4, 10, 23, 43)
 
-        assert_that(start, is_(d(2013, 10, 1, 0, 0, 0)))
+        assert_that(QUARTER.start(some_datetime), is_(d(2013, 10, 1, 0, 0, 0)))