[Python] Performing Union Operation using Inkscape Extension on 3 Groups But Weird Result

I made an extension to perform union operation on each selected group, but I got a weird result.

For example, there are three selected groups of rectangles:



After using the extension on them, only the first group gets converted into a union path, the rest get duplicated and they aren't in their original positions anymore:



The expected result should be three union paths:



Here's the extension (save it as "union_operation_on_each_selected_group.py"):

import inkex
import tempfile, os, shutil
from uuid import uuid4
from inkex import Group, Circle, Ellipse, Line, PathElement, Polygon, Polyline, Rectangle, Use
from inkex.paths import Path
from inkex.command import call
from math import ceil
from lxml import etree

def process_svg(svg, action_string):

temp_folder = tempfile.mkdtemp()

# Create a random filename for svg
svg_temp_filepath = os.path.join(temp_folder, f'original_{str(uuid4())}.svg')

with open(svg_temp_filepath, 'w') as output_file:
svg_string = svg.tostring().decode('utf-8')
output_file.write(svg_string)

processed_svg_temp_filepath = os.path.join(temp_folder, f'processed_{str(uuid4())}.svg')

my_actions = '--actions='

export_action_string = my_actions + f'export-filename:{processed_svg_temp_filepath};{action_string}export-do;'

# Run the command line
cmd_selection_list = inkex.command.inkscape(svg_temp_filepath, export_action_string)

# Replace the current document with the processed document
with open(processed_svg_temp_filepath, 'rb') as processed_svg:
loaded_svg = inkex.elements.load_svg(processed_svg).getroot()

shutil.rmtree(temp_folder)
return loaded_svg

def element_list_union(svg, element_list):

group = None

action_string = ''
for element in element_list:
group = element.getparent()
action_string = action_string + f'select-by-id:{element.get_id()};'
action_string = action_string + f'path-union;select-clear;'
processed_svg = process_svg(svg, action_string)

to_remove = []
for child in group:
to_remove.append(child)
for item in to_remove:
group.remove(item)

for elem in processed_svg:
group.add(elem)

class UnionizeEachGroupMembers(inkex.EffectExtension):

def add_arguments(self, pars):

pars.add_argument("--selection_type_radio", type=str, dest="selection_type_radio", default='all')

def effect(self):

SELECTION_TYPE = self.options.selection_type_radio

if SELECTION_TYPE == 'all':
selection_list = self.svg.descendants()
else:
selection_list = self.svg.selected

# Filter for only shapes
selected_elements = selection_list.filter(inkex.ShapeElement)

if len(selected_elements) < 1:
inkex.errormsg('Please select at least one object / No Objects found')
return

for elem in selected_elements:
if elem.tag == inkex.addNS('g', 'svg'): # Check if the tag is 'g' in the SVG namespace
group = elem
group_id = group.get_id()

elements_to_union = [child for child in group if isinstance(child, (Circle, Ellipse, Line, PathElement, Polygon, Polyline, Rectangle, Use))]

if len(elements_to_union) > 0:
element_list_union(self.svg, elements_to_union)

if __name__ == '__main__':
UnionizeEachGroupMembers().run()


And here's the .inx file:

<?xml version="1.0" encoding="UTF-8"?>
<inkscape-extension xmlns="http://www.inkscape.org/namespace/inkscape/extension">
<name>Union Operation on Each Selected Group</name>
<id>union_operation_on_each_selected_group</id>

<!-- Parameters Here -->

<param name="selection_type_radio" type="optiongroup" appearance="radio" gui-text="Selection Type">
<option value="selected">Selected Objects</option>
<option value="all">All Objects</option>
</param>

<effect>
<object-type>all</object-type>
<effects-menu>
<!-- <submenu name="Submenu Name"/>-->
</effects-menu>
</effect>
<script>
<command location="inx" interpreter="python">union_operation_on_each_selected_group.py</command>
</script>
</inkscape-extension>


You can download the example file here:

Example File

Is it possible to get the expected result using an extension? How could I fix the extension?

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