如何向lxml元素添加属性

Question

I would like to add attribute to a lxml Element like this

<outer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Header>
    <field1 name="blah">some value1</field1>
    <field2 name="asdfasd">some value2</field2>
  </Header>
</outer>

Here is what I have

E = lxml.builder.ElementMaker()    
outer = E.outer
header = E.Header
FIELD1 = E.field1
FIELD2 = E.field2

the_doc = outer(
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance",
    XML_2_HEADER(
        FIELD1('some value1', name='blah'),
        FIELD2('some value2', name='asdfasd'),
        ),
    )

seems like this line is causing some problem

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance",

even if I replace it with

'xmlns:xsi'="http://www.w3.org/2001/XMLSchema-instance",

it won't work.

What is a way to add attribute to lxml Element?

Answer 1

That's a namespace definition, not an ordinary XML attribute. You can pass namespace information to ElementMaker() as a dictionary, for example :

from lxml import etree as ET
import lxml.builder

nsdef = {'xsi':'http://www.w3.org/2001/XMLSchema-instance'}
E = lxml.builder.ElementMaker(nsmap=nsdef)
doc = E.outer(
    E.Header(
        E.field1('some value1', name='blah'),
        E.field2('some value2', name='asdfasd'),
        ),
    )
print ET.tostring(doc, pretty_print=True)

output :

<outer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Header>
    <field1 name="blah">some value1</field1>
    <field2 name="asdfasd">some value2</field2>
  </Header>
</outer>

Link to the docs: http://lxml.de/api/lxml.builder.ElementMaker-class.html