Spans and Trees

A small Python library for converting between XML trees and a span-based structure. This can be useful for extracting sections of text from XML documents and doing special things with some of the tags.

The two main functions are treeToSpans and spansToTrees for converting between an ElementTree element and text with a list of spans. Examples are shown below.

treeToSpans

First create a little example XML tree to convert.

import xml.etree.ElementTree as ET

xmlstring = "<doc><title>Important document</title><contents>Empty</contents></doc>"
root = ET.ElementTree(ET.fromstring(xmlstring)).getroot()

Then use the treeToSpans function to convert the XML document into the text content with spans.

from spans_and_trees import treeToSpans

text, spans = treeToSpans(root)

print(text)  # Important documentEmpty
print(spans) # [(0, 18, 'title', {}), (18, 5, 'contents', {})]

The format of the spans are a tuple of length 4. The element contents are:

1. The start location of the span
2. The length of the span
3. The tag of the span
4. A dictionary of the attributes of the span.

spansToTrees

Now we create a dummy document with a block of text and a span at particular offset.

from spans_and_trees import spansToTree

text = 'The quick brown fox jumped over the lazy dog'
spans = [ (10,5,'colour',{'dummy_attrib':'5'}) ] # The span starts at 10, has length of 5, is a 'colour' tag and has a dummy attribute.

root = spansToTree(text, spans)

print(type(root)) # <class 'xml.etree.ElementTree.Element'>

We can check the XML tree that has been created:

xmlstr = ET.tostring(root)

print(xmlstr) # b'<anon>The quick <colour dummy_attrib="5">brown</colour> fox jumped over the lazy dog</anon>'