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An XML Schema validator and decoder

Project description

The xmlschema library is an implementation of XML Schema for Python (supports Python 2.7 and Python 3.5+).

This library arises from the needs of a solid Python layer for processing XML Schema based files for MaX (Materials design at the Exascale) European project. A significant problem is the encoding and the decoding of the XML data files produced by different simulation software. Another important requirement is the XML data validation, in order to put the produced data under control. The lack of a suitable alternative for Python in the schema-based decoding of XML data has led to build this library. Obviously this library can be useful for other cases related to XML Schema based processing, not only for the original scope.

The full xmlschema documentation is available on “Read the Docs”.


This library includes the following features:

  • Full XSD 1.0 and XSD 1.1 support
  • Building of XML schema objects from XSD files
  • Validation of XML instances against XSD schemas
  • Decoding of XML data into Python data and to JSON
  • Encoding of Python data and JSON to XML
  • Data decoding and encoding ruled by converter classes
  • An XPath based API for finding schema’s elements and attributes
  • Support of XSD validation modes strict/lax/skip
  • Remote attacks protection by default using an XMLParser that forbids entities


Currently the XSD 1.1 validator is provided by class XMLSchema11 and the default XMLSchema class is still an alias of the XSD 1.0 validator, the class XMLSchema10. From version 1.1 of the package the default validator will be linked to the XSD 1.1 validator, a version that will also removes support for Python 2.7.


You can install the library with pip in a Python 2.7 or Python 3.5+ environment:

pip install xmlschema

The library uses the Python’s ElementTree XML library and requires elementpath additional package. The base schemas of the XSD standards are included in the package for working offline and to speed-up the building of schema instances.


Import the library and then create a schema instance using the path of the file containing the schema as argument:

>>> import xmlschema
>>> my_schema = xmlschema.XMLSchema('xmlschema/tests/cases/examples/vehicles/vehicles.xsd')


For XSD 1.1 schemas use the class XMLSchema11, because the default class XMLSchema is still an alias of the XSD 1.0 validator class XMLSchema10. From next minor release (v1.1) the default class will become XMLSchema11.

The schema can be used to validate XML documents:

>>> my_schema.is_valid('xmlschema/tests/cases/examples/vehicles/vehicles.xml')
>>> my_schema.is_valid('xmlschema/tests/cases/examples/vehicles/vehicles-1_error.xml')
>>> my_schema.validate('xmlschema/tests/cases/examples/vehicles/vehicles-1_error.xml')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/brunato/Development/projects/xmlschema/xmlschema/validators/", line 393, in validate
    raise error
xmlschema.validators.exceptions.XMLSchemaValidationError: failed validating <Element '{}cars' at 0x7f8032768458> with XsdGroup(model='sequence').

Reason: character data between child elements not allowed!


  <xs:sequence xmlns:xs="">
        <xs:element maxOccurs="unbounded" minOccurs="0" name="car" type="vh:vehicleType" />


  <vh:cars xmlns:vh="">
    <vh:car make="Porsche" model="911" />
    <vh:car make="Porsche" model="911" />

Using a schema you can also decode the XML documents to nested dictionaries, with values that match to the data types declared by the schema:

>>> import xmlschema
>>> from pprint import pprint
>>> xs = xmlschema.XMLSchema('xmlschema/tests/cases/examples/collection/collection.xsd')
>>> pprint(xs.to_dict('xmlschema/tests/cases/examples/collection/collection.xml'))
{'@xsi:schemaLocation': ' collection.xsd',
 'object': [{'@available': True,
             '@id': 'b0836217462',
             'author': {'@id': 'PAR',
                        'born': '1841-02-25',
                        'dead': '1919-12-03',
                        'name': 'Pierre-Auguste Renoir',
                        'qualification': 'painter'},
             'estimation': Decimal('10000.00'),
             'position': 1,
             'title': 'The Umbrellas',
             'year': '1886'},
            {'@available': True,
             '@id': 'b0836217463',
             'author': {'@id': 'JM',
                        'born': '1893-04-20',
                        'dead': '1983-12-25',
                        'name': 'Joan Miró',
                        'qualification': 'painter, sculptor and ceramicist'},
             'position': 2,
             'title': None,
             'year': '1925'}]}


Davide Brunato and others who have contributed with code or with sample cases.


This software is distributed under the terms of the MIT License. See the file ‘LICENSE’ in the root directory of the present distribution, or

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