A couple years ago I started a series of articles on XML parsing. I covered lxml's etree and Python's included minidom XML parsing library. For whatever reason I didn't notice lxml's objectify sub-package, but I saw it recently and decided I should check it out. To my mind, the objectify module seems to be even more "Pythonic" than etree is. Let's take a some time and go over my old XML examples using objectify and see how it's different!
If you haven't already, go out and download lxml or you won't be able to follow along very well. Once you have it, we can continue. We'll be using the following piece of XML for our parsing pleasure:
1181251680 040000008200E000 1181572063 1800 Bring pizza home 1234360800 1800 Check MS Office website for updates 604f4792-eb89-478b-a14f-dd34d3cc6c21-1234360800 dismissed
Now we need to write some code that can parse and modify the XML. Let's take a look at this little demo that shows a bunch of the neat abilities that objectify provides.
from lxml import etree, objectify
#----------------------------------------------------------------------
def parseXML(xmlFile):
""""""
with open(xmlFile) as f:
xml = f.read()
root = objectify.fromstring(xml)
# returns attributes in element node as dict
attrib = root.attrib
# how to extract element data
begin = root.appointment.begin
uid = root.appointment.uid
# loop over elements and print their tags and text
for appt in root.getchildren():
for e in appt.getchildren():
print "%s => %s" % (e.tag, e.text)
print
# how to change an element's text
root.appointment.begin = "something else"
print root.appointment.begin
# how to add a new element
root.appointment.new_element = "new data"
# print the xml
obj_xml = etree.tostring(root, pretty_print=True)
print obj_xml
# remove the py:pytype stuff
#objectify.deannotate(root)
etree.cleanup_namespaces(root)
obj_xml = etree.tostring(root, pretty_print=True)
print obj_xml
# save your xml
with open("new.xml", "w") as f:
f.write(obj_xml)
#----------------------------------------------------------------------
if __name__ == "__main__":
f = r'path\to\sample.xml'
parseXML(f)
The code is pretty well commented, but we'll spend a little time going over it anyway. First we pass it our sample XML file and objectify it. If you want to get access to a tag's attributes, use the attrib property. It will return a dictionary of the attribute's of the tag. To get to sub-tag elements, you just use dot notation. As you can see, to get to the begin tag's value, we can just do something like this:
begin = root.appointment.begin
If you need to iterate over the children elements, you can use iterchildren. You may have to use a nested for loop structure to get everything. Changing an element's value is as simple as just assigning it a new value. And if you need to create a new element, just add a period and the name of the new element (see below):
root.appointment.new_element = "new data"
When we add or change items using objectify, it will add some annotations to the XML, such as xmlns:py="http://codespeak.net/lxml/objectify/pytype" py:pytype="str". You may not want that included, so you'll have to call the following method to remove that stuff:
etree.cleanup_namespaces(root)
You can also use "objectify.deannotate(root)" to do some deannotation chores, but I wasn't able to get it to work for this example. To save the new XML, you actually seem to need lxml's etree module to convert it to a string so you can save it.
At this point, you should be able to parse most XML documents and edit them effectively with lxml's objectify. I thought it was very intuitive and easy to pick up. Hopefully you will find it useful in your endeavors as well.
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