Crashes when using funcion_plot without h_labels

[Magnun Leno]

When using function_plot like this CairoPlot crashes:

meusdados = lambda x : [1,2,3,4][x]
CairoPlot.function_plot('function4.png', meusdados, 400, 300, grid = True, dots=True, h_bounds=(0,4), step = 1, discrete=True)

After following the execution in the source I found that the problem is in te following pice of render_horz_labels:
if not labels:
        labels = []
        i = self.bounds[HORZ][0]
        while i<self.bounds[HORZ][1]:
            labels.append(str(i*self.step))
            i += (self.bounds[HORZ][1] - self.bounds[HORZ][0])/10
        #labels = [str(i*self.step) for i in range(self.bounds[HORZ][0], self.bounds[HORZ][1])]
    border = self.borders[HORZ]

Testing with h_labels it didn't crashes but the the labels aren't drawn:

meusdados = lambda x : [1,2,3,4][x]
labels = ["a","b","c","d"]
CairoPlot.function_plot('function4.png', meusdados, 400, 300, grid = True, dots=True, h_labels = labels, h_bounds=(0,4), step = 1, discrete=True)

Thanks for this great module!!