Is PyXB's regex XML regex' compliant?

[Sergey Bushmanov]

I am interested in PyXB's behavior matching 'something|empty string'.

I put together a simple example like:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Address">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="City" type="xs:string" />
        <xs:element name="Country" minOccurs="0">
          <xs:simpleType>
            <xs:restriction base="xs:string">
              <xs:pattern value="[A-Z]{2}|" />
            </xs:restriction>
          </xs:simpleType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

with the expectation of element Country to accept either empty string or 2 letter code
(my expectations come from XML regex defintion from https://www.w3.org/TR/xmlschema-2/#regexs

However, when I do:

!pyxbgen -u example_pattern.xsd -m example

import example as e

address = e.Address()

address.City = "New-York"
address.Country = "USA"

I'm getting 3-letter Country code accepted and the following xml file produced:

<Address>
  <City>New-York</City>
  <Country>USA</Country>
</Address>

So, my question is: is PyXB's regex engine XML compliant?

A little bit of background:

1. I got patterns like "[A-Z]{2}|" from xmlSpy generated XSD's.
2. The above mentioned pattern does not validate either through xmllint or lxml (both throw an error that this is not a valid regex pattern)
3. I've asked a related question on stackoverflow and got some replies there.

[Sergey Bushmanov]

Well, the answer to my problem is brackets:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Address">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="City" type="xs:string" />
        <xs:element name="Country" minOccurs="0">
          <xs:simpleType>
            <xs:restriction base="xs:string">
              <xs:pattern value="([A-Z]{2}|)" />
            </xs:restriction>
          </xs:simpleType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

After putting the pattern in brackets it works as expected.

[Peter A. Bigot]

PyXB attempts to translate XML regex syntax into Python syntax for execution. It's intended to be correct; if it isn't please open a ticket on github.

[Sergey Bushmanov]

I will. As a temporal remedy, can you please point me to the file where this translation happens?

[Peter A. Bigot]

https://github.com/pabigot/pyxb/blob/next/pyxb/utils/xmlre.py