Writing just the xml declaration to file using Python

Question

I am writing multiple xml files in python by looping over lists of strings. Suppose I have:

from xml.etree.ElementTree import ElementTree, Element, SubElement, tostring

parent = Element('parent')
child = SubElement(parent, 'child')
f = open('file.xml', 'w')
document = ElementTree(parent)
l = ['a', 'b', 'c']
for ch in l:
    child.text = ch
    document.write(f, encoding='utf-8', xml_declaration=True)

The output:

<?xml version='1.0' encoding='utf-8'?>
<parent><child>a</child></parent><?xml version='1.0' encoding='utf-8'?>
<parent><child>b</child></parent><?xml version='1.0' encoding='utf-8'?>
<parent><child>c</child></parent>

Desired output:

<?xml version='1.0' encoding='utf-8'?>
<parent>
<child>a</child>
<child>b</child>
<child>c</child>
</parent>

I only want the xml declaration to appear one time, at the top of the file. Probably should write the declaration to the file before the loop, but when I attempt that, I get empty elements. I do not want to do this:

f.write('<?xml version='1.0' encoding='utf-8'?>')

How to write just to xml declaration to the file?

Edit: Desired output

Amirshk · Accepted Answer · 2015-01-09 00:44:47Z

6

You need to add the SubItems to the tree before writing the file. In your code you overwritten the same element and wrote the entire XML document in every iteration of the loop.

Also, your XML syntax is missing a top-level "root" element to be valid.

from xml.etree.ElementTree import ElementTree, Element, SubElement, tostring

root = Element('root')

l = ['a', 'b', 'c']
for ch in l:
    parent = SubElement(root,'parent')
    child = SubElement(parent, 'child')
    child.text = ch

document = ElementTree(root)
document.write('file.xml', encoding='utf-8', xml_declaration=True)

and the output will be:

<?xml version='1.0' encoding='utf-8'?>
<root>
  <parent><child>a</child></parent>
  <parent><child>b</child></parent>
  <parent><child>c</child></parent>
</root>

answered Jan 9, 2015 at 0:44

Amirshk

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Comments

Philip · Accepted Answer · 2015-01-09 00:41:19Z

1

I am not familiar with Python's XML libraries, but let's take a step back. If you do what you want, your output will not be valid XML. XML must have exactly one root element.

So, you could have:

<?xml version='1.0' encoding='utf-8'?>
<uberparent>
<parent><child>a</child></parent>
<parent><child>b</child></parent>
<parent><child>c</child></parent>
</uberparent>

Supposing you're creating a Google site map, for example: their schema says that the root element is "urlset".

answered Jan 9, 2015 at 0:41

Philip

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Comments

Anzel · Accepted Answer · 2015-01-09 01:06:44Z

0

This is technically doable by just setting a bool() flag on xml_declaration:

parent = Element('parent')
child = SubElement(parent, 'child')
f = open('file.xml', 'w')
document = ElementTree(parent)
l = ['a', 'b', 'c']
# use enumerate to have (index, element) pair, started from 0
for i, ch in enumerate(l):
    child.text = ch
    # Start index=0, since bool(0) is Fale, and bool(1..n) is True
    # the flag will be offset
    document.write(f, encoding='utf-8', xml_declaration=bool(not i))
f.close()

Updated:

Since OP has realised the desired ouput is incorrect in syntax, and changed the requirement, here is the normal way to deal with xml:

from xml.etree.ElementTree import ElementTree, Element, SubElement, tostring

parent = Element('parent')
f = open('file.xml', 'w')
document = ElementTree(parent)
l = ['a', 'b', 'c']
for ch in l:
    child = SubElement(parent, 'child')
    child.text = ch
document.write(f, encoding='utf-8', xml_declaration=True)
f.close()

edited Jan 9, 2015 at 1:06

answered Jan 9, 2015 at 0:39

Anzel

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1 Comment

Anzel Over a year ago

Although as a side note, just like what @Amirshk mentioned, this is not a valid xml syntax

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