CODEWITHSUNDEEP
pythonxmlserializationxml-parsingelementtree
user1159517
user1159517

Reputation: 6350

How to serialize python ElementTree in ordered fashion of xml nodes?

I have an in-memory python XML ElementTree which looks like

<A>
  <B>..</B>
  <C>..</C>
  <D>..</D>
</A>

I serialize the ElementTree into xml by 

xmlstr = minidom.parseString(ET.tostring(root)).toprettyxml("  ")

The order of the inner nodes B,C,D changes every time i invoke the above tostring() method. How can i make sure my serialization will follow a deterministic order?

Upvotes: 3

Views: 2385

Answers (1)

Tomalak
Tomalak

Reputation: 338406

I realize many answers here suggest this, but 

minidom.parseString(ET.tostring(root)).toprettyxml("  ")

is actually a really horrible way of pretty-printing an XML file.

It involves parsing, serializing with ET and then parsing again and serializing again with a completely different XML library. It's silly and wasteful and I would not be surprised if minidom messes it up.

If you have it installed, switch to lxml and use its built-in pretty-printing function.

If you are for some reason stuck with xml.etree.ElementTree, you can use a simple recursive function to prettify a tree in-place:

# xmlhelpers.py

# taken from http://effbot.org/zone/element-lib.htm#prettyprint
def indent(elem, level=0):
    i = "\n" + level*"  "
    if len(elem):
        if not elem.text or not elem.text.strip():
            elem.text = i + "  "
        if not elem.tail or not elem.tail.strip():
            elem.tail = i
        for elem in elem:
            indent(elem, level+1)
        if not elem.tail or not elem.tail.strip():
            elem.tail = i
    else:
        if level and (not elem.tail or not elem.tail.strip()):
            elem.tail = i

Usage is straight-forward:

import xml.etree.ElementTree as ET
from xmlhelpers import indent    

root = ET.fromstring("<A><B>..</B><C>..</C><D>..</D></A>")
indent(root)

print( ET.tostring(root) )

This prints a nicely indented version:

b'<A>\n  <B>..</B>\n  <C>..</C>\n  <D>..</D>\n</A>\n'

That being said, never use "tostring" to write an XML tree to a file.

Always write XML files with the functions provided by the XML library.

tree = ET.ElementTree(root) # only necessary if you don't already have a tree
tree.write(filename, encoding="UTF-8")

Upvotes: 2

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