Python writing to an xml file

Question

I am trying to write to an xml file. I have changed a specific element in my code, and am able to get it to print successfully. I need to have it written to the file, without changing the structure of the file.
My code:

import os
from lxml import etree


directory = '/Users/eeamesX/work/data/expert/EFTlogs/20160725/IT'
XMLParser = etree.XMLParser(remove_blank_text=True)
for f in os.listdir(directory):
    if f.endswith(".xml"):

        xmlfile = directory + '/' + f



        tree = etree.parse(xmlfile, parser=XMLParser)
        root = tree.getroot()

        hardwareRevisionNode = root.find(".//hardwareRevision")



        if hardwareRevisionNode.text == "5":
            print " "
            print "Old Tag: " + hardwareRevisionNode.text

            x = hardwareRevisionNode.text = "DVT2"

            print "New Tag " +  hardwareRevisionNode.text

When I try various methods of opening and closing the file, it just deletes all the data in the xml file. Using this method

outfile = open(xmlfile, 'w')
oufile.write(etree.tostring(tree))
outfile.close()

Changed the code structure of my file to be one long line.

There are pretty printers or indenters in lxml. One long string is perfectly valid xml. See this question http://stackoverflow.com/questions/749796/pretty-printing-xml-in-python — WombatPM, Aug 26 '16 at 18:15

score 2 · Answer 1 · edited May 23 '17 at 12:14

2

To get newlines in the output file, it looks like you need to pass pretty_print=True to your sterilization (write or tostring) call.

Side note; Normally, when you open files with python you open them like this:

with open('filename.ext', 'mode') as myfile:
    myfile.write(mydata)

This way there is less risk of file descriptor leaks. The tree.write("filename.xml") method looks like a nice and easy way to avoid dealing with the file entirely.

edited May 23 '17 at 12:14

Community

1
1

answered Aug 26 '16 at 17:59

pnovotnak

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tree = etree.parse(xmlfile, parser=XMLParser) root = tree.getroot() tree.write(xmlfile) hardwareRevisionNode = root.find(".//hardwareRevision") – Anekdotin Aug 26 '16 at 18:01
Changing to that results in the file being made into one line, and the text not being replaced – Anekdotin Aug 26 '16 at 18:02
In the above snippet you are re-saving the original tree. See my edited answer for the newline problem. – pnovotnak Aug 26 '16 at 18:06
It corrected the one line, but it doesnt write to the actual file. It still says 5, instead of DVT3 – Anekdotin Aug 26 '16 at 18:14
tree = etree.parse(xmlfile, parser=XMLParser) root = tree.getroot() tree.write(xmlfile, pretty_print=True) hardwareRevisionNode = root.find(".//hardwareRevision") – Anekdotin Aug 26 '16 at 18:16

score 2 · Accepted Answer · answered Aug 26 '16 at 18:11

If you are wanting to replace a value within an existing XML file then use:

tree.write(xmlfile)

Currently you are simply overwriting your file entirely and using the incorrect method (open()). tree.write() is normally what you would want to use. It might look something like this:

tree = etree.parse(xmlfile, parser=XMLParser)
root = tree.getroot()
hardwareRevisionNode = root.find(".//hardwareRevision")
if hardwareRevisionNode.text == "5":
    print "Old Tag: " + hardwareRevisionNode.text
    hardwareRevisionNode.text = "DVT2"
    print "New Tag: " +  hardwareRevisionNode.text
    tree.write(xmlfile)

↳ https://docs.python.org/2/library/xml.etree.elementtree.html

I needed to put it at the bottom and it worked flawlessly – Anekdotin Aug 26 '16 at 18:30 — Anekdotin, Aug 26 '16 at 18:30

Python writing to an xml file

2 Answers2