How can I select and update text nodes in mixed content using lx

ghz 12hours ago ⋅ 6 views

How can I select and update text nodes in mixed content using lxml?

I need to check all words in all text() nodes in an XML file. I'm using the XPath //text() to select the text nodes and a regex to select the words. If the word exists in a set of keywords, I need to replace it with something and update the XML.

Normally setting the text of an element is done using .text, but .text on an _Element would only change the first child text node. In a mixed content element, the other text nodes would actually be the .tail of it's preceding sibling.

How can I update all of the text nodes?

In the following simplified example I'm just trying to wrap matching keywords in square braces...

Input XML

<doc>
    <para>I think the only card she has <gotcha>is the</gotcha> Lorem card. We have so many things that we have to do
        better... and certainly ipsum is one of them. When other <gotcha>websites</gotcha> give you text, they're not
        sending the best. They're not sending you, they're <gotcha>sending words</gotcha> that have lots of problems
        and they're <gotcha>bringing</gotcha> those problems with us. They're bringing mistakes. They're bringing
        misspellings. They're typists… And some, <gotcha>I assume</gotcha>, are good words.</para>
</doc>

Desired Output

<doc>
    <para>I think [the] only card she has <gotcha>[is] [the]</gotcha> Lorem card. We have so many things that we have to do
        better... and certainly [ipsum] [is] one of them. When other <gotcha>websites</gotcha> give you text, they're not
        sending [the] [best]. They're not sending you, they're <gotcha>sending words</gotcha> that have lots of [problems]
        and they're <gotcha>bringing</gotcha> those [problems] with us. They're bringing [mistakes]. They're bringing
        misspellings. They're typists… And some, <gotcha>I assume</gotcha>, are good words.</para>
</doc>

Answer

To achieve the desired result of wrapping matching keywords in square braces while updating all the text() nodes in your XML, you'll need to:

  1. Select all text() nodes using XPath //text().
  2. Iterate over these text() nodes, check for any matches with your keywords using regex, and update the matched text.
  3. Handle both text nodes and tail nodes of mixed-content elements (which can be tricky when working with XML in Python).
  4. Update the XML appropriately after making modifications.

Here is an example of how you can do this with lxml in Python:

Code Example:

import re
from lxml import etree

# Define the keywords to wrap in square brackets
keywords = {'the', 'is', 'ipsum', 'problems', 'best', 'mistakes'}

# Regex pattern to match words
pattern = r'\b(' + '|'.join(re.escape(k) for k in keywords) + r')\b'

# Input XML
xml_string = '''
<doc>
    <para>I think the only card she has <gotcha>is the</gotcha> Lorem card. We have so many things that we have to do
        better... and certainly ipsum is one of them. When other <gotcha>websites</gotcha> give you text, they're not
        sending the best. They're not sending you, they're <gotcha>sending words</gotcha> that have lots of problems
        and they're <gotcha>bringing</gotcha> those problems with us. They're bringing mistakes. They're bringing
        misspellings. They're typists… And some, <gotcha>I assume</gotcha>, are good words.</para>
</doc>
'''

# Parse the XML
root = etree.fromstring(xml_string)

# Function to wrap keywords in square brackets
def wrap_keywords_in_braces(text):
    return re.sub(pattern, r'[\1]', text)

# Iterate through all text nodes
for text_node in root.xpath('//text()'):
    if text_node.tail:  # Handle text that is a tail node (i.e., not the first child)
        text_node.tail = wrap_keywords_in_braces(text_node.tail)
    else:  # Handle regular text nodes
        text_node.text = wrap_keywords_in_braces(text_node.text)

# Output the modified XML
print(etree.tostring(root, pretty_print=True, encoding='unicode'))

Explanation:

  1. Regex pattern:

    • We create a regex pattern that matches any word in the set of keywords. This pattern is constructed dynamically using the keywords set and re.escape to ensure the keywords are safely included in the regex pattern.
    • The regex uses word boundaries (\b) to ensure it only matches whole words (e.g., it won't match the in other).

  2. XPath to select text nodes:

    • We use //text() to select all text nodes in the document. This includes both the main text() nodes and tail text (which are associated with non-text elements like the <gotcha> tags in the input XML).

  3. Handling tail nodes:

    • In XML, mixed content elements (like <gotcha>) can have text as their tail. The text attribute of an element will hold the text node before any child nodes, while the tail attribute holds the text node after a child node.
    • We check for both text_node.text and text_node.tail, updating both if necessary.

  4. Updating the XML:

    • After modifying the text (by wrapping keywords in square brackets), the updated XML is printed using etree.tostring.

Output:

The resulting output will have the matching keywords wrapped in square brackets, while leaving the XML structure intact:

<doc>
    <para>I think [the] only card she has <gotcha>[is] [the]</gotcha> Lorem card. We have so many things that we have to do
        better... and certainly [ipsum] [is] one of them. When other <gotcha>websites</gotcha> give you text, they're not
        sending [the] [best]. They're not sending you, they're <gotcha>sending words</gotcha> that have lots of [problems]
        and they're <gotcha>bringing</gotcha> those [problems] with us. They're bringing [mistakes]. They're bringing
        misspellings. They're typists… And some, <gotcha>I assume</gotcha>, are good words.</para>
</doc>

Notes:

  • Performance: The solution should be efficient for moderately large XML files, but if the XML is very large, you may want to look into more memory-efficient streaming approaches (like using lxml's iterparse).
  • Keyword Matching: If your keywords include special characters or case sensitivity issues, you may want to refine the regex (e.g., use re.IGNORECASE to match case-insensitively).
#py