Addin multiple sub-elements with same tag to en XML tree with Python/Elementtree

Question

I am reading data from a python dictionary and trying to add more book elements in the below tree. Below is just an examplke, i need to copy an element with it's child(s) but replace the content, in this case i need to copy the book element but replace title and author.

  <store>
    <bookstore>
        <book>
            <title lang="en">IT book</title>
            <author>Some IT Guy</author>
        </book>
    </bookstore>
  </store>

I use this code:

root = et.parse('Template.xml').getroot()
bookstore = root.find('bookstore')
book = root.find('bookstore').find('book')

Then i run the loop through a dictionary and trying to add new book elements under the bookstore:

for bk in bks:
    book.find('title').text = bk
    bookstore.append(book)

The result is that book elements are added to the bookstore, however they all contain title from the last iteration of the loop. I know i am doing something wrong here, but i can't understand what. I tried:

book[0].append(book) and book[-1].append(book)

But it did not help.

Chertkov Pavel · Accepted Answer · 2018-03-13 16:29:08Z

3

You changing the same object.

You need to actual copy the object with copy.deepcopy

Example:

import xml.etree.ElementTree as et
import copy

root = et.parse('Template.xml').getroot()
bookstore = root.find('bookstore')
book = root.find('bookstore').find('book')

bks = ["book_title_1", "book_title_2", "book_title_3"]
for bk in bks:
   new_book = copy.deepcopy(book)
   new_book.find('title').text = bk
   bookstore.append(new_book)

print et.tostring(root)

answered Mar 13, 2018 at 16:29

Chertkov Pavel

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2 Comments

Alex D. Over a year ago

Thanks a lot, Pavel. I have suspected that my way to copy the element was the root cause of issue! I tried your example and it worked right away!

kushy Over a year ago

I thought the tag being the same name was preventing from adding multiple tags with same name, but apparently, I was wrong. I'm amazed that this works. Thanks! :-)

Cavaz · Accepted Answer · 2018-03-13 16:48:34Z

2

I'm guessing instead of books.append(book) you mean bookstore.append(book).

Basically here you have a structure:

- store
  - bookstore
    - book
      - book infos

with book = root.find('bookstore').find('book') you are actually getting a reference to the (only) one you already have, and in the loop you keep updating its title and re-appending it to the store (so basically you are only overwriting the title). What you must do is to create every time a new Element (or clone it as Chertkov Pavel suggested, but you must remember to overwrite all the fields, or you may end up inheriting the wrong author) and append it to the bookstore:

for bk in bks:
    new_book = et.Element('book')

    # create and append title
    new_title = et.Element('title', attib={'lang':'eng'})
    new_title.text = bk
    new_book.append(new_title)

    # add also author and any other info
    # ...

    # append to the bookstore
    bookstore.append(new_book)

print et.tostring(root)

edited Mar 13, 2018 at 16:48

answered Mar 13, 2018 at 16:39

Cavaz

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1 Comment

Alex D. Over a year ago

Thanks for the clear explanation. From the behavior i was sure it behaves as you explained, but i did not know to overcome this issue.

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