Test the existence of an Element with lxml.objectify

lxml, lxml.objectify, python, xml

Solution

`find` method will return `None` if the element does not exist.

>>> xml = '''<?xml version="1.0" encoding="utf-8"?>
... <Test>
...   <MyElement1>sdfsdfdsfd</MyElement1>
... </Test>'''
>>>
>>> from lxml import objectify
>>> root = objectify.fromstring(xml)
>>> root.find('.//MyElement1')
'sdfsdfdsfd'
>>> root.find('.//MyElement17')
>>> root.find('.//MyElement17') is None
True

UPDATE according to the question edit:

>>> from lxml import objectify
>>>
>>> def add_string(parent, attr, s):
...     if len(attr) == 1:
...         setattr(parent, attr[0], s)
...     else:
...         child = getattr(parent, attr[0], None)
...         if child is None:
...             child = objectify.SubElement(parent, attr[0])
...         add_string(child, attr[1:], s)
...
>>> root = objectify.fromstring(xml)
>>> add_string(root, ['MyElement1', 'Blah'], 'New')
>>> add_string(root, ['MyElement17', 'Blah'], 'New')
>>> add_string(root, ['MyElement1', 'Foo', 'Bar'], 'Hello')
>>>
>>> root.MyElement1.Blah
'New'
>>> root.MyElement17.Blah
'New'
>>> root.MyElement1.Foo.Bar
'Hello'

Problem

What is the standard way for testing if an element exists or not with `lxml.objectify` ? Sample XML : ``` <?xml version="1.0" encoding="utf-8"?> <Test> <MyElement1>sdfsdfdsfd</MyElement1> </Test> ``` Code ``` from lxml import etree, objectify with open('config.xml') as f: xml = f.read() root = objectify.fromstring(xml) print root.MyElement1 print root.MyElement17 # AttributeError: no such child: MyElement17 ``` Then, what is the simplest solution to write something on a specific path ? ``` root.MyElement1.Blah = 'New' # this works because MyElement1 already exists root.MyElement17.Blah = 'New' # this doesn't work because MyElement17 doesn't exist root.MyElement1.Foo.Bar = 'Hello' # this doesn't as well... How to do this shortly ? ```

Original source