Solved

How do I insert an XML fragment into another XML tree using Python and lxml?

Posted on 2014-07-29
4
954 Views
Last Modified: 2014-07-29
I have a fragment of XML (the output from an XSL transform using lxml.etree), which I want to add to another XML tree.  I have
  <newsection>
    <newitem name="fred" attr1="7"/> 
    <newitem name="george" attr1="6"/>
  </newsection>

Open in new window

and
<oldparent>
  <oldsection>
    <oldchild>
      <oldgc name="sally"/>
    </oldchild>
  </oldsection>
  <othersect>
    <otherch name="alice"/>
  </othersect>
</oldparent>

Open in new window

Essentially, I need to insert the first fragment within the second so that "<newsection" is at the same level as "<oldsection>" and "<othersect>".  the location doesn't matter.

So far, I have tried inserting the first fragment entry by entry, but it ends up in the wrong order.  For example, using
#!/usr/bin/env python

import lxml.etree as ET

sd = ET.parse('file_containing_first_fragment.xml')
ft = ET.parse('extract_first_fragment.xsl')
transform = ET.XSLT(ft)
rx = transform(sd)
# "rx" now contains just the first fragment

st = ET.parse('second_fragment.xml')
root = st.getroot()
for e in rx.getiterator():
	root.append(e)
print(ET.tostring(st))

Open in new window

This does insert the first fragment, but the ordering is wrong - I get the "<newsection>" open and close before any of the "<newitem>" entries:
<oldparent>
  <oldsection>
    <oldchild>
      <oldgc name="sally"/>
    </oldchild>
  </oldsection>
  <othersect>
    <otherch name="alice"/>
  </othersect>
<newsection>
       </newsection>
<newitem name="fred" attr1="7"/> 
    <newitem name="george" attr1="6"/>
</oldparent>

Open in new window

How can I do this and have that "<newsection>" fragment in the right order?
0
Comment
Question by:simon3270
  • 2
  • 2
4 Comments
 
LVL 28

Accepted Solution

by:
pepr earned 500 total points
ID: 40226402
The following code is with the standard xml.etree.ElementTree, but it should be the same with the lxml:
#!python3

import xml.etree.ElementTree as ET

rx = ET.fromstring('''
<newsection>
  <newitem name="fred" attr1="7"/> 
  <newitem name="george" attr1="6"/>
</newsection>''')
# "rx" now contains just the first fragment

root = ET.fromstring('''
<oldparent>
  <oldsection>
    <oldchild>
      <oldgc name="sally"/>
    </oldchild>
  </oldsection>
  <othersect>
    <otherch name="alice"/>
  </othersect>
</oldparent>''')

root.append(rx)
ET.dump(root)

Open in new window

It prints
<oldparent>
  <oldsection>
    <oldchild>
      <oldgc name="sally" />
    </oldchild>
  </oldsection>
  <othersect>
    <otherch name="alice" />
  </othersect>
<newsection>
  <newitem attr1="7" name="fred" />
  <newitem attr1="6" name="george" />
</newsection></oldparent>

Open in new window

The root stores the element 'oldparent' as the list of its children. You want to append the rx element as another child (as a whole).
0
 
LVL 19

Author Comment

by:simon3270
ID: 40226537
Thanks, @pepr, you pointed me in the right direction.

Your example works fine with lxml.etree, but my code didn't - I got:
  File "./tstsd.py", line 13, in <module>
    root.append(rx)
AttributeError: 'lxml.etree._ElementTree' object has no attribute 'append'

My problem turned out to be that ET.parse (which I was using to read the XML file) returns an ElementTree, which doesn't have an "append" attribute. ET.fromstring (which you used) returns an Element, which does have one.

The fix was to make use the string attributes to make ElementTrees into Elements, so I did
    root = ET.parse('second_fragment.xml')
    root = ET.tostring(ET.fromstring(root))
Not pretty, but it worked!
0
 
LVL 28

Expert Comment

by:pepr
ID: 40226626
No, no! It is known that ET.parse() returns a tree object. The root element object is obtained from the tree object via calling its .getroot() method -- as you did in your code for example here:
...
st = ET.parse('second_fragment.xml')
root = st.getroot()

Open in new window

0
 
LVL 19

Author Comment

by:simon3270
ID: 40226960
Aha, even easier!  And certainly prettier. Many thanks.
0

Featured Post

How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

Join & Write a Comment

Variable is a place holder or reserved memory locations to store any value. Which means whenever we create a variable, indirectly we are reserving some space in the memory. The interpreter assigns or allocates some space in the memory based on the d…
Flask is a microframework for Python based on Werkzeug and Jinja 2. This requires you to have a good understanding of Python 2.7. Lets install Flask! To install Flask you can use a python repository for libraries tool called pip. Download this f…
Learn the basics of lists in Python. Lists, as their name suggests, are a means for ordering and storing values. : Lists are declared using brackets; for example: t = [1, 2, 3]: Lists may contain a mix of data types; for example: t = ['string', 1, T…
Learn the basics of modules and packages in Python. Every Python file is a module, ending in the suffix: .py: Modules are a collection of functions and variables.: Packages are a collection of modules.: Module functions and variables are accessed us…

757 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

18 Experts available now in Live!

Get 1:1 Help Now