Check for the existence of an element with lxml.objectify

Question

What is the standard way to check for the presence or absence of an element using lxml.objectify ?

XML example:

 <?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 for writing something in a particular way?

 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 ? 

Answer 1

find method will return None if the item 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:

 >>> 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' 

Answer 2

You can use getattr :

 if getattr(root, 'MyElement17', None): # do something