How can lxml validate some XML against both an XSD file while also loading an inline schema too?

Question

I'm having problems getting lxml to successfully validate some xml. The XSD schema and XML file are both from Amazon documentation so should be compatible. But the XML itself refers to another schema that's not being loaded.

Here is my code, which is based on the lxml validation tutorial:

xsd_doc = etree.parse('ProductImage.xsd')
xsd = etree.XMLSchema(xsd_doc)
xml = etree.parse('ProductImage_sample.xml')
xsd.validate(xml)
print xsd.error_log

"ProductImage_sample.xml:2:0:ERROR:SCHEMASV:SCHEMAV_CVC_ELT_1: Element 'AmazonEnvelope': No matching global declaration available for the validation root."

I get no errors if I validate against amzn-envelope.xsd instead of ProductImage.xsd, but that defeats the point of seeing if a given Image feed is valid. All xsd & xml files mentioned are in my working directory along with my python script by the way.

Here is a snippet of the sample xml, which should definately be valid:

<?xml version="1.0"?>
<AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
    <Header>
        <DocumentVersion>1.01</DocumentVersion>
        <MerchantIdentifier>Q_M_STORE_123</MerchantIdentifier>
    </Header>
    <MessageType>ProductImage</MessageType>
    <Message>
        <MessageID>1</MessageID>
        <OperationType>Update</OperationType>
        <ProductImage>
            <SKU>1234</SKU>

Here is a snippet of the schema (this file is not public so I can't show all of it):

<?xml version="1.0"?>
<!-- Revision="$Revision: #5 $" -->
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
    <xsd:include schemaLocation="amzn-base.xsd"/>
    <xsd:element name="ProductImage">
        <xsd:complexType>
            <xsd:sequence>
                <xsd:element ref="SKU"/>

I can say that following the include to amzn-base.xsd does not end up reaching a definition of the AmazonEnvelope tag. So my questions is: can lxml load schemas via a tag like <AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">. And if not, how can I validate my Image feed?

Answer 1

The answer is I should validate by the parent schema file, which as mentioned at the top of the XML file is amzn-envelope.xsd as this contains the line:

<xsd:include schemaLocation="ProductImage.xsd"/>

In general then, lxml won't read such a declaration as xsi:noNamespaceSchemaLocation="amzn-envelope.xsd" but if you can find the parent schema to validate against then this should hopefully include the specific schema you're interested in.