Editing values in a xml file with Python

Question

Hey. I want to have a config.xml file for settings in a Python web app.

I made car.xml manually. It looks like this:

<car>
    <lights>
        <blinkers>off</blinkers>
    </lights>
</car>

Now I want to see whether the blinkers are on or off, using xml.etree.ElementTree.

import xml.etree.ElementTree as ET
tree = ET.parse('car.xml')
blinkers = tree.findtext('lights/blinkers')
print blinkers
> off

Now I want to turn the blinkers on and off, how can I do this?

Answer 1

XML is a rather poor way of storing configuration settings. For one, XML is not exactly human friendly in the context of settings. In the Python universe in particular you are better off using a settings module (as @AaronMcSmooth commented). Unfortunately a lot of projects in the Java world have (mis?)used XML for settings thereby making it a trend. I'd argue that this trend really sucks. Use native settings (module in Python) or something more human friendly like YAML.

Answer 2

You can remove nodes by calling the parent node's remove method, and insert nodes by calling ET.SubElement:

import xml.etree.ElementTree as ET

def flip_lights(tree):
    lights = tree.find('lights')
    state=get_blinker(tree)
    blinkers = tree.find('lights/blinkers')
    lights.remove(blinkers)
    new_blinkers = ET.SubElement(lights, "blinkers")
    new_blinkers.text='on' if state=='off' else 'off'

def get_blinker(tree):
    blinkers = tree.find('lights/blinkers')
    return blinkers.text

tree = ET.parse('car.xml')
print(get_blinker(tree))
# off
flip_lights(tree)
print(get_blinker(tree))
# on
flip_lights(tree)
print(get_blinker(tree))
# off
flip_lights(tree)
print(get_blinker(tree))
# on
tree.write('car2.xml')

Answer 3

Without addressing the merits of using XML instead of a Python module for managing configuration files, here's how to do what you asked using lxml:

>>> from lxml import etree
>>> xml = """<car>
   <lights>
      <blinkers>on</blinkers>
   </lights>
</car>"""
>>> doc = etree.fromstring(xml)
>>> elm = doc.xpath("/car/lights/blinkers")[0]
>>> elm.text="off"
>>> etree.tostring(doc)
'<car>\n   <lights>\n      <blinkers>off</blinkers>\n   </lights>\n</car>'

Answer 4

Take a look at this article.

But consider AaronMcSmooth's comment above -- this may be the wrong approach to your overall problem.

Answer 5

Use beautifulstonesoup. Here is the section on modifying xml:

http://www.crummy.com/software/BeautifulSoup/documentation.html#Modifying%20the%20Parse%20Tree