import lxml.etree
html = '<div> <div id="abc 123"></div> <div id="def hhh"></div> <div id="ghi test"></div> </div>'
root = lxml.etree.fromstring(html)
print root.xpath(".//div[starts-with(@id, 'def')]")[0].attrib
aW1wb3J0IGx4bWwuZXRyZWUKaHRtbCA9ICc8ZGl2PiA8ZGl2IGlkPSJhYmMgMTIzIj48L2Rpdj4gPGRpdiBpZD0iZGVmIGhoaCI+PC9kaXY+IDxkaXYgaWQ9ImdoaSB0ZXN0Ij48L2Rpdj4gPC9kaXY+Jwpyb290ID0gbHhtbC5ldHJlZS5mcm9tc3RyaW5nKGh0bWwpCiAKcHJpbnQgcm9vdC54cGF0aCgiLi8vZGl2W3N0YXJ0cy13aXRoKEBpZCwgJ2RlZicpXSIpWzBdLmF0dHJpYg==