lxml处理xml时的字符编码问题

<?xml version="1.0" encoding="gbk"?>
<DOCUMENT>
<da><![CDATA[中文，就是任性]]></da>
</DOCUMENT>

lxml.etree.XMLSyntaxError: Extra content at the end of the document

tst = u&#39;<?xml version="1.0" encoding="gbk"?><DOCUMENT><da><![CDATA[中文，就是任性]]></da></DOCUMENT>&#39;
for event,element in etree.iterparse(BytesIO(tst.encode(&#39;utf-8&#39;))):
    print("%s, %s" % (element.tag, element.text))

lxml.etree.XMLSyntaxError: input conversion failed due to input error, bytes 0x8B 0x2C 0xE6 0x9D

tst = u&#39;<?xml version="1.0" encoding="gbk"?><DOCUMENT><da><![CDATA[中文，就是任性]]></da></DOCUMENT>&#39;
tst = tst.replace(&#39;encoding="gbk"&#39;, &#39;encoding="utf-8"&#39;)
for event,element in etree.iterparse(BytesIO(tst.encode(&#39;utf-8&#39;))):
    print("%s, %s" % (element.tag, element.text))

da, 中文，就是任性
DOCUMENT, None