Validating with an XML schema in Python

I am assuming you mean using XSD files. Surprisingly there aren't many python XML libraries that support this. lxml does however. Check Validation with lxml. The page also lists how to use lxml to validate with other schema types.

You can easily validate an XML file or tree against an XML Schema (XSD) with the xmlschema Python package. It's pure Python, available on PyPi and doesn't have many dependencies.

Example - validate a file:

import xmlschema
xmlschema.validate('doc.xml', 'some.xsd')

The method raises an exception if the file doesn't validate against the XSD. That exception then contains some violation details.

If you want to validate many files you only have to load the XSD once:

xsd = xmlschema.XMLSchema('some.xsd')
for filename in filenames:
    xsd.validate(filename)

If you don't need the exception you can validate like this:

if xsd.is_valid('doc.xml'):
    print('do something useful')

Alternatively, xmlschema directly works on file objects and in memory XML trees (either created with xml.etree.ElementTree or lxml). Example:

import xml.etree.ElementTree as ET
t = ET.parse('doc.xml')
result = xsd.is_valid(t)
print('Document is valid? {}'.format(result))

The PyXB package at http://pyxb.sourceforge.net/ generates validating bindings for Python from XML schema documents. It handles almost every schema construct and supports multiple namespaces.

lxml provides etree.DTD

from the tests on http://lxml.de/api/lxml.tests.test_dtd-pysrc.html

...
root = etree.XML(_bytes("<b/>")) 
dtd = etree.DTD(BytesIO("<!ELEMENT b EMPTY>")) 
self.assert_(dtd.validate(root)) 

import xmlschema


def get_validation_errors(xml_file, xsd_file):
    schema = xmlschema.XMLSchema(xsd_file)
    validation_error_iterator = schema.iter_errors(xml_file)
    errors = list()
    for idx, validation_error in enumerate(validation_error_iterator, start=1):
        err = validation_error.__str__()
        errors.append(err)
        print(err)
    return errors

errors = get_validation_errors('sample3.xml', 'sample_schema.xsd')