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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def contextDoc(self):
 """Get the doc from an xpathContext """

        ret = libxml2mod.xmlXPathGetContextDoc(self._o)
        if ret is None:raise xpathError('xmlXPathGetContextDoc() failed')
        __tmp = xmlDoc(_obj=ret)
        return __tmp