XML (.xsd) feed validation against a schema

Question

I have a XML file and I have a XML schema. I want to validate the file against that schema and check if it adheres to that. I am using python but am open to any language for that matter if there is no such useful library in python.

What would be my best options here? I would worry about the how fast I can get this up and running.

Answer 1

Definitely lxml.

Define an XMLParser with a predefined schema, load the the file fromstring() and catch any XML Schema errors:

from lxml import etree

def validate(xmlparser, xmlfilename):
    try:
        with open(xmlfilename, 'r') as f:
            etree.fromstring(f.read(), xmlparser) 
        return True
    except etree.XMLSchemaError:
        return False

schema_file = 'schema.xsd'
with open(schema_file, 'r') as f:
    schema_root = etree.XML(f.read())

schema = etree.XMLSchema(schema_root)
xmlparser = etree.XMLParser(schema=schema)

filenames = ['input1.xml', 'input2.xml', 'input3.xml']
for filename in filenames:
    if validate(xmlparser, filename):
        print("%s validates" % filename)
    else:
        print("%s doesn't validate" % filename)

Note about encoding

If the schema file contains an xml tag with an encoding (e.g. <?xml version="1.0" encoding="UTF-8"?>), the code above will generate the following error:

Traceback (most recent call last):
  File "<input>", line 2, in <module>
    schema_root = etree.XML(f.read())
  File "src/lxml/etree.pyx", line 3192, in lxml.etree.XML
  File "src/lxml/parser.pxi", line 1872, in lxml.etree._parseMemoryDocument
ValueError: Unicode strings with encoding declaration are not supported. Please use bytes input or XML fragments without declaration.

A solution is to open the files in byte mode: open(..., 'rb')

[...]
def validate(xmlparser, xmlfilename):
    try:
        with open(xmlfilename, 'rb') as f:
[...]
with open(schema_file, 'rb') as f:
[...]

Answer 2

The python snippet is good, but an alternative is to use xmllint:

xmllint -schema sample.xsd --noout sample.xml

Answer 3

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