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?

Solution

Problem is because it exports all elements to processed svg and later it puts all elements in group.

I had to use select-invert to invert selection and delete to delete other elements, and later select-all to select again previous elements to run path-union. This way it exports only one object. Or rather 3 elements: group with path (create by path-union)(I don't know why it create extra group) and two other elements but they are not displayed but I don't know what it is.

Full working code:

For test I used temporary folder with prefix inkex_ and skiped shutil.rmtree() so I could easily check what it wrote in proccesed file.

I also first create list with all commands and later convert them to one string using
action_string = ";".join(action_commands). It allowed me to add new commands in easy way.
(I tested also export-id and export-id-only but it doesn't export page size and later objects are in wrong place)

And old elements can be removed from group using one command group.clear()

I was thinking to add elements to group.getparent() instead of group because currently it creates two nested groups - original group (in which were selected items) and extra group from processed file.

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

msg = inkex.errormsg  # to have shorter command to write

def process_svg(svg, action_commands):

    temp_folder = tempfile.mkdtemp(prefix='inkex_')

    # --- keep original ---

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

    msg(f"{original_svg_temp_filepath = }")

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

    # --- create new ---

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

    action_commands.append(f'export-filename:{processed_svg_temp_filepath}')
    action_commands.append('export-do')

    action_string = ";".join(action_commands)

    my_actions = f'--actions={action_string}'

    msg(f"{my_actions = }")

    # Run the command line
    cmd_selection_list = inkex.command.inkscape(original_svg_temp_filepath, my_actions)

    # --- load new ---

    # 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):
    msg(f"{len(element_list) = }")

    group = None

    action_commands = []

    for element in element_list:
        group = element.getparent()
        #msg(f"{group = }")
        action_commands.append(f'select-by-id:{element.get_id()}')

    action_commands.append('select-invert')
    action_commands.append('delete')
    action_commands.append('select-all')
    action_commands.append('path-union')
    #action_commands.append('select-clear')

    processed_svg = process_svg(svg, action_commands)

    #msg(f"{len(group) = }")
    group.clear()
    #msg(f"{len(group) = }")

    msg(f"{len(processed_svg) = }")

    for elem in processed_svg:
        #msg(f"{elem = }")
        group.add(elem)
        #group.getparent().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

        msg(selection_list)
        # 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()

Extra information if someone would be interested.

Extension Tutorial - Inkscape Tutorial
List of avaliable commands: inkscape --action-list
There is shell inkscape --shell but I didn't test it.