Schema fails to validate: '' is not a valid value of the atomic type 'xs:int'

[Rotem]

Recently started failing with the following code:

---
from lxml import etree
SCHEMA = """<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
   attributeFormDefault="unqualified">
  <xs:element name="testsuite" type="testsuite"/>
  <xs:complexType name="testsuite">
    <xs:attribute name="errors" type="xs:int">
    </xs:attribute>
  </xs:complexType>
</xs:schema>"""

schema_root = etree.XML(SCHEMA)
schema = etree.XMLSchema(schema_root)

XML = """
<testsuite errors="0"></testsuite>
"""
xml = etree.fromstring(XML, parser=etree.XMLParser(schema=schema))
---

I get:

XMLSyntaxError: Element 'testsuite', attribute 'errors': '' is not a valid value of the atomic type 'xs:int'

Python            : sys.version_info(major=3, minor=5, micro=2, releaselevel='final', serial=0)
lxml.etree          : (3, 6, 1, 0)
libxml used         : (2, 9, 4)
libxml compiled     : (2, 9, 4)
libxslt used        : (1, 1, 29)
libxslt compiled    : (1, 1, 29)

[Ronald Dilley (ronald-d-dilley-jr)]

I'm getting a nearly identical issue to this bug, except with xs:float values versus xs:int.

Does not seem to be present in 3.6.0 or 3.6.1.
Definitely in version 3.6.4.
Have not tried 3.6.2 or 3.6.3.

[Hans-Thomas (htmue-h)]

The bug seems to be related to libxml 2.9.4.

I see the bug with lxml-3.6.0 and lxml-3.6.4 linked against libxml2-2.9.4
but not when using libxml2-2.9.3.

Validation fails also for boolean attributes.

Moreover the bug appears only when using a validating parser. Validating a document parsed with a non-validating parser works fine.

[Caleb Morse (morse-caleb)]

This bug appears to have been fixed by libmx2 in this commit: https://git.gnome.org/browse/libxml2/commit/?id=3169602058bd2d04913909e869c61d1540bc7fb4, and was reported here: https://bugzilla.gnome.org/show_bug.cgi?id=766834.

They haven't released a new version with that bugfix yet though.

[scoder (scoder)]

(Most) binary wheels of lxml 4.0.0 come with libxml2 2.9.5, which should resolve this issue.