Insert xml node in specific location

Question

I would like to build the following xml:

<Item>
    <Name>Hello</Name>
    <Date>2014-01-01</Date>
    <Hero>1</Helo>
</Item>

Given the following code structure, how would I insert the <Date> node before the hero node?

item = etree.SubElement(self.xml_node, 'Item')
etree.SubElement(item, 'Name').text = 'Hello'
etree.SubElement(item, 'Hero').text = 1
# Now, how to insert the 'Date' element before the Hero element?

Answer 1

Using etree.SubElement always appends the subelement to the end of the parent item. So instead, to insert a new element at a particular location, use item.insert(pos, subelement):

import lxml.etree as etree
xml_node = etree.Element("node")
item = etree.SubElement(xml_node, 'Item')
etree.SubElement(item, 'Name').text = 'Hello'
etree.SubElement(item, 'Hero').text = '1'
etree.SubElement(item, 'Date').text = '2014-01-01'
item.insert(1, item[-1])
print(etree.tostring(xml_node, pretty_print=True))

yields

<node>
  <Item>
    <Name>Hello</Name>
    <Date>2014-01-01</Date>
    <Hero>1</Hero>
  </Item>
</node>

---

Each node in an ElementTree can occur at only one place. So although

etree.SubElement(item, 'Date').text = '2014-01-01'

places the <Date> node at the end of <item>,

item.insert(1, item[-1])

moves the last node in item, i.e. the <Date> node, to position 1 (making it the second child in <Item>).