Added a new kind of Graph : DateY

DateY is approximatively the same as XY but is uses
datetime.datetime as X values (and prints date format x-axis labels)
w

pygal/graph/__init__.py

@@ -35,5 +35,6 @@ CHARTS_NAMES = [
     'Pyramid',
     'VerticalPyramid',
     'Dot',
-    'Gauge'
+    'Gauge',
+    'DateY'
 ]

pygal/graph/datey.py

@@ -0,0 +1,107 @@
+# -*- coding: utf-8 -*-
+# This file is proposed as a part of pygal
+# A python svg graph plotting library
+#
+# A python svg graph plotting library
+# Copyright © 2012 Snarkturne  (modified from Kozea XY class)
+#
+# This library is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation, either version 3 of the License, or (at your option) any
+# later version.
+#
+# This library is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with pygal. If not, see <http://www.gnu.org/licenses/>.
+
+"""
+DateY graph
+
+Example :
+
+
+"""
+
+
+from pygal.util import compute_scale
+from pygal.graph.line import Line
+from pygal.graph.xy import XY 
+import datetime
+
+class DateY(XY):
+    """ DateY Graph """
+    _offset=datetime.datetime(year=2000,month=1,day=1)
+    def _todate(self, d) :
+        """ Converts  a number to a date """
+        return str(self._offset+datetime.timedelta(seconds=d))
+    def _tonumber(self,d) :
+        """ Converts a date to a number """
+        if d==None: return None
+        return  (d-self._offset).total_seconds()
+
+    def _get_value(self, values, i):
+        return 'x=%s, y=%s' % (self._todate(values[i][0]),self._format(values[i][1]))
+
+    def _compute(self):
+        # Approximatively the same code as in XY.
+        # The only difference is the transformation of dates to numbers
+        # (beginning) and the reversed transforamtion to dates (end)
+        self._offset = min([val[0]
+                 for serie in self.series
+                 for val in serie.values
+                 if val[0] is not None])
+        for serie in self.series :
+            serie.values=[(self._tonumber(v[0]),v[1]) for v in serie.values]
+        
+        xvals = [val[0]
+                 for serie in self.series
+                 for val in serie.values
+                 if val[0] is not None]
+        yvals = [val[1]
+                 for serie in self.series
+                 for val in serie.values
+                 if val[1] is not None]
+        if xvals:
+            xmin = min(xvals)
+            xmax = max(xvals)
+            rng = (xmax - xmin)
+        else:
+            rng = None
+
+        for serie in self.series:
+            serie.points = serie.values
+            if self.interpolate and rng:
+                vals = list(zip(*sorted(
+                    [t for t in serie.points if None not in t], key=lambda x: x[0])))
+                serie.interpolated = self._interpolate(
+                    vals[1], vals[0], xy=True, xy_xmin=xmin, xy_rng=rng)
+
+        if self.interpolate and rng:
+            xvals = [val[0]
+                     for serie in self.series
+                     for val in serie.interpolated]
+            yvals = [val[1]
+                     for serie in self.series
+                     for val in serie.interpolated]
+            if xvals:
+                xmin = min(xvals)
+                xmax = max(xvals)
+                rng = (xmax - xmin)
+            else:
+                rng = None
+
+        if rng:
+            self._box.xmin, self._box.xmax = min(xvals), max(xvals)
+            self._box.ymin, self._box.ymax = min(yvals), max(yvals)
+
+        x_pos = compute_scale(
+            self._box.xmin, self._box.xmax, self.logarithmic, self.order_min)
+        y_pos = compute_scale(
+            self._box.ymin, self._box.ymax, self.logarithmic, self.order_min)
+
+        self._x_labels = list(zip(list(map(self._todate, x_pos)), x_pos))
+        self._y_labels = list(zip(list(map(self._format, y_pos)), y_pos))

pygal/util.py

@@ -333,7 +333,7 @@ def prepare_values(raw, config, cls):
             else:
                 value = raw_value
 
-            if cls.__name__ == 'XY':
+            if cls.__name__ == 'XY' or cls.__name__ == 'DateY':
                 if value is None:
                     value = (None, None)
                 elif not hasattr(value, '__iter__'):