code to validate xml agains XSD schema with no network access.

validate_xmlschema_no_network.py

import os
from lxml import etree


def validate_xml_with_schema( xml_filepath: str, xsd_filepath: str ) -> None:
    """
    Validates an XML file against an XSD schema, without network access.
    Confirms that:
    - xmlcatalog is routing the schema location to the local file system
    - the C `libxml2` library used by lxml does auto-default to the standard server's `xml/catalog` file.
        - so this should not be necessary: ```os.environ['XML_CATALOG_FILES'] = '/path/to/xml/catalog'```
    """
    schema_obj = etree.XMLSchema( etree.XML(open(xsd_filepath, 'rb').read()) )
    parser_obj = etree.XMLParser( schema=schema_obj, no_network=True )
    try:
        etree.parse( xml_filepath, parser_obj )  # since the parser is buil with the schema, it will auto-validate the XML, no need for `schema.assertValid( doc )`
        print( "XML is valid according to the schema." )
    except etree.DocumentInvalid as e:
        print( f"XML validation error: {e}" )
    return