'Add a whole pie to the chart.
Args:
points: A list of pie segment sizes
labels: A list of labels for the pie segments
colors: A list of colors for the segments. Missing colors will be chosen
automatically.
Return:
The index of the newly added pie.'

def AddPie(self, points, labels=None, colors=None):

    num_colors = len((colors or []))
    num_labels = len((labels or []))
    pie_index = len(self.data)
    self.data.append([])
    for (i, pt) in enumerate(points):
        label = None
        if (i < num_labels):
            label = labels[i]
        color = None
        if (i < num_colors):
            color = colors[i]
        self.AddSegment(pt, label=label, color=color, pie_index=pie_index)
    return pie_index
