"extend" not working python "ElementTree" example

Example 1: python elementtree build xml

import xml.etree.cElementTree as ET

root = ET.Element("root")
doc = ET.SubElement(root, "doc")

ET.SubElement(doc, "field1", name="blah").text = "some value1"
ET.SubElement(doc, "field2", name="asdfasd").text = "some vlaue2"

tree = ET.ElementTree(root)
tree.write("filename.xml")

Example 2: how to open xml file element tree

import xml.etree.ElementTree as ET

tree = ET.parse('filename.xml') #this gets the file into a tree structure
tree_root = tree.getroot() #this gives us the root element of the file