inst.xml

<!DOCTYPE dtd [
 <!ENTITY file SYSTEM "some_file">
]>

<SomeObject xmlns="some_ns">
  <d>2013-07-15T20:21:43.476838</d>
  <i>5</i>
  <s>&file;</s>
</SomeObject>

py_output

Traceback (most recent call last):
  File "validation_internal_error.py", line 31, in <module>
    schema.validate(elt)
  File "lxml.etree.pyx", line 3252, in lxml.etree._Validator.validate (src/lxml/lxml.etree.c:143796)
  File "xmlschema.pxi", line 151, in lxml.etree.XMLSchema.__call__ (src/lxml/lxml.etree.c:152165)
lxml.etree.XMLSchemaValidateError: Internal error in XML Schema validation.

schema.xsd

<xs:schema xmlns:wsa="http://schemas.xmlsoap.org/ws/2003/03/addressing" xmlns:tns="some_ns" xmlns:plink="http://schemas.xmlsoap.org/ws/2003/05/partner-link/" 
xmlns:xop="http://www.w3.org/2004/08/xop/include" xmlns:soap12env="http://www.w3.org/2003/05/soap-envelope/" xmlns:senc="http://schemas.xmlsoap.org/soap/encoding/" 
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:senv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:soap12enc="http://www.w3.org/2003/05/soap-encoding/" 
targetNamespace="some_ns" elementFormDefault="qualified">
  <xs:complexType name="SomeObject">
    <xs:sequence>
      <xs:element name="d" type="xs:dateTime" minOccurs="0" nillable="true"/>
      <xs:element name="i" type="xs:integer" minOccurs="0" nillable="true"/>
      <xs:element name="s" type="xs:string" minOccurs="0" nillable="true"/>
    </xs:sequence>
  </xs:complexType>
  <xs:element name="SomeObject" type="tns:SomeObject"/>
</xs:schema>

sh_output

inst.xml:5: namespace warning : xmlns: URI some_ns is not absolute
<SomeObject xmlns="some_ns">
                           ^
<?xml version="1.0"?>
<!DOCTYPE dtd [
<!ENTITY file SYSTEM "some_file">
]>
<SomeObject xmlns="some_ns">
  <d>2013-07-15T20:21:43.476838</d>
  <i>5</i>
  <s>&file;</s>
</SomeObject>
inst.xml:8: element s: Schemas validity error : Internal error: xmlSchemaVDocWalk, there is at least one entity reference in the node-tree currently being validated. Processing of entities with this XML Schema processor is not supported (yet). Please substitute entities before validation..
inst.xml validation generated an internal error

some_file

some_file_contents

validation_internal_error.py

#!/usr/bin/env python

from lxml.etree import XMLParser, fromstring, XMLSchema

schema_doc = open('schema.xsd').read()
inst_doc = open('inst.xml').read()

parser = XMLParser(resolve_entities=False)
elt = fromstring(inst_doc, parser)
schema = XMLSchema(fromstring(schema_doc))
schema.validate(elt)

validation_internal_error.sh

#!/bin/sh

xmllint --schema schema.xsd inst.xml