Implement Monthly scale and add a bunch of tests.

CHANGELOG.rst

@@ -1,7 +1,9 @@
 0.3.0
 -----
 
-* Implement :class:`.Annual` scale type.
+* Expanded unit tests for :class:`.Scale` subclasses.
+* Implemented :class:`.Monthly` scale type.
+* Implemented :class:`.Annual` scale type.
 * Zero lines now render above other tick marks. (#31)
 * Fixed rendering of :class:`.Bar` and :class:`.Column` shapes for negative values. (#52)
 * Refactored the :class:`.Lattice` API.

leather/__init__.py

@@ -6,7 +6,7 @@
 from leather.grid import Grid
 from leather.lattice import Lattice
 from leather.legend import Legend
-from leather.scales import Scale, Annual, Linear, Ordinal, Temporal
+from leather.scales import Scale, Annual, Linear, Monthly, Ordinal, Temporal
 from leather.series import Series, key_function
 from leather.shapes import Shape, Bars, Columns, Dots, Lines, style_function
 from leather import theme

leather/scales/__init__.py

@@ -3,5 +3,6 @@
 from leather.scales.annual import Annual
 from leather.scales.base import Scale
 from leather.scales.linear import Linear
+from leather.scales.monthly import Monthly
 from leather.scales.ordinal import Ordinal
 from leather.scales.temporal import Temporal

leather/scales/annual.py

@@ -1,13 +1,15 @@
 #!/usr/bin/env python
 
 from datetime import datetime, date
+from decimal import Decimal
+import math
 
 from leather.scales.temporal import Temporal
 
 
 class Annual(Temporal):
     """
-    A scale that maps years to a pixel range.
+    A scale that maps years to a coordinate range.
 
     This scale takes linear values (dates, datetimes, or numbers), but treats
     them as ordinal values for purposes of projection. Thus you can use this
@@ -28,7 +30,7 @@ def _value_as_date(self, value):
         """
         if isinstance(value, (datetime, date)):
             return value
-        elif isinstance(value, (int, float)):
+        elif isinstance(value, (int, float, Decimal)):
             return date(value, 1, 1)
 
         raise ValueError('Unsupported domain value for Annual scale.')
@@ -44,7 +46,12 @@ def project(self, value, range_min, range_max):
 
         pos = d.year - self._min.year
 
-        return range_min + ((pos + 0.5) * segment_size)
+        if pos >= 0:
+            pos += 0.5
+        else:
+            pos -= 0.5
+
+        return range_min + (pos * segment_size)
 
     def project_interval(self, value, range_min, range_max):
         """
@@ -68,7 +75,15 @@ def ticks(self, count):
         """
         Generate a series of ticks for this scale.
         """
-        return [date(year, 1, 1) for year in range(self._min.year, self._max.year + 1)]
+        size = int(math.ceil(float(self._max.year - self._min.year) / count))
+        values = []
+
+        for i in range(count):
+            years = self._min.year + (i * size)
+
+            values.append(date(years, 1, 1))
+
+        return values
 
     def format_tick(self, value, i, count):
         """

leather/scales/temporal.py

@@ -1,5 +1,9 @@
 #!/usr/bin/env python
 
+from datetime import datetime
+
+import six
+
 from leather.scales.base import Scale
 
 
@@ -20,7 +24,19 @@ def project(self, value, range_min, range_max):
         """
         Project a value in this scale's domain to a target range.
         """
-        pos = (value - self._min) / (self._max - self._min)
+        numerator = value - self._min
+        denominator = self._max - self._min
+
+        # Python 2 does not support timedelta division
+        if six.PY2:
+            if isinstance(self._min, datetime):
+                numerator = numerator.total_seconds()
+                denominator = denominator.total_seconds()
+            else:
+                numerator = float(numerator.days)
+                denominator = float(denominator.days)
+
+        pos = numerator / denominator
 
         return ((range_max - range_min) * pos) + range_min
 

test.py

@@ -4,14 +4,15 @@
 
 data = [
     (datetime.date(2010, 1, 1), -1),
-    (datetime.date(2011, 1, 1), -1),
-    (datetime.date(2012, 1, 1), 0),
+    (datetime.date(2010, 6, 1), 0),
+    (datetime.date(2011, 1, 1), -0.5),
+    (datetime.date(2012, 1, 1), 0.5),
     (datetime.date(2013, 1, 1), 1)
 ]
 
 chart = leather.Chart()
 chart.add_columns(data)
 chart.add_lines(data)
 chart.add_dots(data)
-chart.set_x_scale(leather.Annual(datetime.date(2010, 1, 1), datetime.date(2014, 1, 1)))
+chart.set_x_scale(leather.Monthly(datetime.date(2010, 1, 1), datetime.date(2014, 1, 1)))
 chart.to_svg('test.svg')

tests/test_scales.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python
 
+from datetime import date, datetime
+
 try:
     import unittest2 as unittest
 except ImportError:
@@ -43,3 +45,148 @@ def test_ticks(self):
 
         self.assertEqual(scale.ticks(5), [0, 2.5, 5, 7.5, 10])
         self.assertEqual(scale.ticks(6), [0, 2, 4, 6, 8, 10])
+
+
+class TestOrdinal(XMLTest):
+    def test_project(self):
+        scale = leather.Ordinal(['a', 'b', 'c', 'd'])
+
+        self.assertEqual(scale.project('b', 0, 20), 7.5)
+
+        scale = leather.Ordinal(['a', 'd', 'c', 'b'])
+
+        self.assertEqual(scale.project('b', 0, 20), 17.5)
+
+    def test_project_interval(self):
+        scale = leather.Ordinal(['a', 'b', 'c', 'd'])
+
+        self.assertEqual(scale.project_interval('b', 0, 20), (5.25, 9.75))
+
+        scale = leather.Ordinal(['a', 'd', 'c', 'b'])
+
+        self.assertEqual(scale.project_interval('b', 0, 20), (15.25, 19.75))
+
+    def test_ticks(self):
+        scale = leather.Ordinal(['a', 'b', 'c', 'd'])
+
+        self.assertEqual(scale.ticks(4), ['a', 'b', 'c', 'd'])
+        self.assertEqual(scale.ticks(5), ['a', 'b', 'c', 'd'])
+        self.assertEqual(scale.ticks(6), ['a', 'b', 'c', 'd'])
+
+
+class TestTemporal(XMLTest):
+    """
+    Note: due to leap-year calculations, it's almost impossible to write
+    exact tests for this scale which are not trivial.
+    """
+    def test_project(self):
+        scale = leather.Temporal(date(2010, 1, 1), date(2014, 1, 1))
+
+        self.assertAlmostEqual(scale.project(date(2011, 1, 1), 0, 20), 5, 1)
+        self.assertAlmostEqual(scale.project(date(2012, 1, 1), 0, 20), 10, 1)
+        self.assertAlmostEqual(scale.project(date(2009, 1, 1), 0, 20), -5, 1)
+
+        scale = leather.Temporal(datetime(2010, 1, 1), datetime(2014, 1, 1))
+
+        self.assertAlmostEqual(scale.project(datetime(2011, 1, 1), 0, 20), 5, 1)
+        self.assertAlmostEqual(scale.project(datetime(2012, 1, 1), 0, 20), 10, 1)
+        self.assertAlmostEqual(scale.project(datetime(2009, 1, 1), 0, 20), -5, 1)
+
+    def test_project_interval(self):
+        scale = leather.Temporal(date(2010, 1, 1), date(2014, 1, 1))
+
+        with self.assertRaises(NotImplementedError):
+            scale.project_interval(date(2011, 1, 1), 0, 20)
+
+    def test_ticks(self):
+        scale = leather.Temporal(date(2010, 1, 1), date(2014, 1, 1))
+
+        ticks = scale.ticks(5)
+        self.assertEqual(ticks[0], date(2010, 1, 1))
+        self.assertEqual(ticks[-1], date(2014, 1, 1))
+
+
+class TestAnnual(XMLTest):
+    def test_project(self):
+        scale = leather.Annual(date(2010, 1, 1), date(2014, 1, 1))
+
+        self.assertEqual(scale.project(date(2011, 1, 1), 0, 20), 6)
+        self.assertEqual(scale.project(date(2012, 1, 1), 0, 20), 10)
+        self.assertEqual(scale.project(date(2009, 1, 1), 0, 20), -6)
+
+        scale = leather.Annual(datetime(2010, 1, 1), datetime(2014, 1, 1))
+
+        self.assertEqual(scale.project(datetime(2011, 1, 1), 0, 20), 6)
+        self.assertEqual(scale.project(datetime(2012, 1, 1), 0, 20), 10)
+        self.assertEqual(scale.project(datetime(2009, 1, 1), 0, 20), -6)
+
+        scale = leather.Annual(2010, 2014)
+
+        self.assertEqual(scale.project(2011, 0, 20), 6)
+        self.assertEqual(scale.project(2012, 0, 20), 10)
+        self.assertEqual(scale.project(2009, 0, 20), -6)
+
+    def test_project_interval(self):
+        scale = leather.Annual(date(2010, 1, 1), date(2014, 1, 1))
+
+        self.assertEqual(scale.project_interval(date(2011, 1, 1), 0, 20), (4.2, 7.8))
+
+    def test_ticks(self):
+        scale = leather.Annual(date(2010, 1, 1), date(2014, 1, 1))
+
+        self.assertEqual(scale.ticks(5), [
+            date(2010, 1, 1),
+            date(2011, 1, 1),
+            date(2012, 1, 1),
+            date(2013, 1, 1),
+            date(2014, 1, 1)
+        ])
+
+
+class TestMonthly(XMLTest):
+    """
+    See notes for :class:`.TestTemporal`.
+    """
+    def test_project(self):
+        scale = leather.Monthly(date(2010, 1, 1), date(2014, 1, 1))
+
+        self.assertAlmostEqual(scale.project(date(2011, 1, 1), 0, 48), 12, 0)
+        self.assertAlmostEqual(scale.project(date(2012, 1, 1), 0, 48), 24, 0)
+        self.assertAlmostEqual(scale.project(date(2008, 12, 1), 0, 48), -12, 0)
+
+        scale = leather.Monthly(datetime(2010, 1, 1), datetime(2014, 1, 1))
+
+        self.assertAlmostEqual(scale.project(datetime(2011, 1, 1), 0, 48), 12, 0)
+        self.assertAlmostEqual(scale.project(datetime(2012, 1, 1), 0, 48), 24, 0)
+        self.assertAlmostEqual(scale.project(datetime(2008, 12, 1), 0, 48), -12, 0)
+
+        with self.assertRaises(ValueError):
+            scale = leather.Monthly(2010, 2014)
+
+    def test_project_interval(self):
+        scale = leather.Monthly(date(2010, 1, 1), date(2014, 1, 1))
+
+        a, b = scale.project_interval(date(2011, 1, 1), 0, 48)
+        self.assertAlmostEqual(a, 11.5, 0)
+        self.assertAlmostEqual(b, 12.5, 0)
+
+    def test_ticks(self):
+        scale = leather.Monthly(date(2010, 1, 1), date(2014, 1, 1))
+
+        self.assertEqual(scale.ticks(5), [
+            date(2010, 1, 1),
+            date(2011, 1, 1),
+            date(2012, 1, 1),
+            date(2013, 1, 1),
+            date(2014, 1, 1)
+        ])
+
+        scale = leather.Monthly(date(2010, 1, 1), date(2012, 1, 1))
+
+        self.assertEqual(scale.ticks(5), [
+            date(2010, 1, 1),
+            date(2010, 7, 1),
+            date(2011, 1, 1),
+            date(2011, 7, 1),
+            date(2012, 1, 1)
+        ])