Using dates in a simple plot with wxPython doesn't work

I try to use a dates on the x-aches. With pure Python3 code it works
fine. BUt when I try to use this inside wxPython application on a
FigureCanvas it doesn't work. And I don't understand the difference
here.

This is the error
[err]
    plot.plot([datetime.date(2015, 1, 7),
TypeError: descriptor 'date' requires a 'datetime.datetime' object but
received a 'int'
[/err]

This is the fine working pure Python3 code.
[code]
#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import matplotlib.pyplot as plt
import datetime

plt.plot([datetime.date(2015, 1, 7),
    datetime.date(2015, 2, 5),
    datetime.date(2015, 6, 2)],
   [70.3, 60.1, 68.8])
plt.show()
[/code]

This is the piece of wxPython code that cause the error
[code]
# -*- coding: utf-8 -*-
import matplotlib.pyplot as pyplot
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as
FigureCanvas
from datetime import datetime

#...

class StatisticTab(wx.Panel):
    def __init__(self, parent):
        super(StatisticTab, self).__init__(parent)

        panel = wx.Panel(self)

        fig = pyplot.figure()
        plot = self.fig.add_subplot(1,1,1)
        plot.plot([datetime.date(2015, 1, 7),
                   datetime.date(2015, 2, 5),
                   datetime.date(2015, 6, 2)],
                  [70.3, 60.1, 68.8])

        self.canvas = FigureCanvas(self, -1, fig)

        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(panel)
        self.SetSizer(sizer)
[/code]