Python 如何在Visual Studio 2013中调用类MyWindow（Window）内的函数？

我正在使用VS2013和PTVS，我想按下一个按钮来调用一个函数。但是我是python和WPF的初学者，所以我遇到了一些麻烦，所以我的函数类是：

class VendasXML(object):
    def MakeXML(self) :
        offset = 0
        url = 'https://api.mercadolibre.com/orders/search?seller=' + AutenticacaoML["user_id"] + '&access_token=' + AutenticacaoML["access_token"] + '&offset=' + str(offset)
        response = urllib2.urlopen(url)
        b = response.read()

        bjson = json.loads(b)
        total = str(bjson['paging']['total'])
        limit = str(bjson['paging']['limit'])
        total = int(total)
        limit = int(limit)
        i = 0
        TotalRec = 0
        Totalt = 0

和我的类MyWindow（窗口）：

我在按钮标签中调用WPF中的函数：

<Button Click="AtualizarXML" x:Name="butao" Content="Button" Grid.Column="1" HorizontalAlignment="Left" Margin="519,79,-381,0" VerticalAlignment="Top" Width="371" Height="323"/>

但是，当我单击按钮调用函数时，会出现以下异常：

---

我必须做些什么来克服这个问题？

我找到了解决方案：

def MakeXML(user) :
    offset = 0
    url = 'https://api.mercadolibre.com/orders/search?seller=' + user["user_id"] + '&access_token=' + user["access_token"] + '&offset=' + str(offset)
    print(url)
    response = urllib2.urlopen(url)
    b = response.read()
    print(b)

    bjson = json.loads(b)
    total = str(bjson['paging']['total'])
    limit = str(bjson['paging']['limit'])
    total = int(total)
    limit = int(limit)
    i = 0
    TotalRec = 0
    Totalt = 0

以及：

def MakeXML(user) :
    offset = 0
    url = 'https://api.mercadolibre.com/orders/search?seller=' + user["user_id"] + '&access_token=' + user["access_token"] + '&offset=' + str(offset)
    print(url)
    response = urllib2.urlopen(url)
    b = response.read()
    print(b)

    bjson = json.loads(b)
    total = str(bjson['paging']['total'])
    limit = str(bjson['paging']['limit'])
    total = int(total)
    limit = int(limit)
    i = 0
    TotalRec = 0
    Totalt = 0

def AtualizarXML(self, sender, e):
    MakeXML(AutenticacaoML())