How to use the pyexiv2.XmpTag function in pyexiv2

def __setitem__(self,key,value):
        try:
            pyexiv2.ImageMetadata.__setitem__(self,key,value)
        except TypeError:
            if key.startswith('Exif'):
                value=pyexiv2.ExifTag(key,value)
            elif key.startswith('Iptc'):
                value=pyexiv2.IptcTag(key,value)
            elif key.startswith('Xmp'):
                value=pyexiv2.XmpTag(key,value)
            pyexiv2.ImageMetadata.__setitem__(self,key,value)

try:
                pluginobject[KeyTag].values = KeyValue

            except KeyError:
                pluginobject[KeyTag] = pyexiv2.IptcTag(KeyTag, KeyValue)

            except (ValueError, AttributeError):
                pass

        # Xmp KeyValue family?
        elif "Xmp" in KeyTag:
            try:
                pluginobject[KeyTag].values = KeyValue

            except KeyError:
                pluginobject[KeyTag] = pyexiv2.XmpTag(KeyTag, KeyValue)

            except (ValueError, AttributeError):
                pass

def set_tag_multiple(self, tag, value):
        if tag.startswith('Iptc'):
            new_tag = pyexiv2.IptcTag(tag, value)
        elif tag.startswith('Xmp'):
            new_tag = pyexiv2.XmpTag(tag)
            if new_tag.type == 'Lang Alt':
                new_tag = pyexiv2.XmpTag(tag, {'x-default': value[0]})
            elif new_tag.type == 'Date':
                new_tag.raw_value = value[0]
            else:
                new_tag = pyexiv2.XmpTag(tag, value)
        self._md[tag] = new_tag

def set_tag_multiple(self, tag, value):
        if tag.startswith('Iptc'):
            new_tag = pyexiv2.IptcTag(tag, value)
        elif tag.startswith('Xmp'):
            new_tag = pyexiv2.XmpTag(tag)
            if new_tag.type == 'Lang Alt':
                new_tag = pyexiv2.XmpTag(tag, {'x-default': value[0]})
            elif new_tag.type == 'Date':
                new_tag.raw_value = value[0]
            else:
                new_tag = pyexiv2.XmpTag(tag, value)
        self._md[tag] = new_tag

def set_tag_multiple(self, tag, value):
        if tag.startswith('Iptc'):
            new_tag = pyexiv2.IptcTag(tag, value)
        elif tag.startswith('Xmp'):
            new_tag = pyexiv2.XmpTag(tag)
            if new_tag.type == 'Lang Alt':
                new_tag = pyexiv2.XmpTag(tag, {'x-default': value[0]})
            elif new_tag.type == 'Date':
                new_tag.raw_value = value[0]
            else:
                new_tag = pyexiv2.XmpTag(tag, value)
        self._md[tag] = new_tag