Bug report

Bug description:

Since gh-156665, Node.cloneNode(), Document.importNode() and Attr.cloneNode() raise xml.dom.NamespaceErr for DOM Level 1 nodes that have a colon in the name. Such nodes have no namespace and are created by createElement("svg:rect"), createAttribute("a:b"), setAttribute("xmlns:xsi", ...), or by parsing with namespace processing disabled.

from xml.dom import minidom

doc = minidom.Document()
root = doc.appendChild(doc.createElement("root"))
root.setAttribute("xmlns:xsi", "http://www.w3.org/2001/XMLSchema-instance")
root.appendChild(doc.createElement("svg:rect"))
for label, func in [
    ("cloneNode", lambda: root.cloneNode(True)),
    ("importNode", lambda: minidom.Document().importNode(root, True)),
    ("Attr.cloneNode", lambda: doc.createAttribute("a:b").cloneNode(True)),
]:
    try:
        node = func()
    except Exception as exc:
        print(f"{label}: {type(exc).__name__}: {exc}")
    else:
        print(f"{label}: {node.nodeName}")

Output on main:

cloneNode: NamespaceErr: cannot use the prefix 'xmlns' with an empty namespace
importNode: NamespaceErr: cannot use the prefix 'xmlns' with an empty namespace
Attr.cloneNode: NamespaceErr: cannot use the prefix 'a' with an empty namespace

Expected, as in 3.15 and earlier:

cloneNode: root
importNode: root
Attr.cloneNode: a:b

_clone_node() creates the clones with createElementNS(), setAttributeNS() and createAttributeNS(), and these now reject a prefixed name when the namespace is empty. A plain setAttribute("xmlns", ...) fails the same way, because the xmlns attribute is only allowed in the XMLNS namespace.

CPython versions tested on:

CPython main branch (3.13 and 3.12 are not affected)

Operating systems tested on:

Windows

Linked PRs

• gh-158978: Fix cloning of DOM Level 1 nodes in xml.dom.minidom #158987