[xml.dom.minidom] nodeValue attr is not defined on Node class but directly on all derived classes #100710

dylan-robins · 2023-01-03T13:19:28Z

[xml.dom.minidom] nodeValue attr is not defined on Node class but directly on all derived classes

According to the documentation, the Node class is supposed to have an attribute nodeValue that "has a different meaning for each node type; see the DOM specification for details.. [...] The value is a string or None."". However, this attribute is undefined on the Node class, but is then implemented on all derived classes (DocumentFragment, Attr, Element, ProcessingInstruction, CharacterData, DocumentType, Entity, Notation, Document).

As a result, IDEs and static analysers raise false positives when analysing "correct" code.

from xml.dom import minidom

dummy_xml: str = """<?xml version="1.0"?>
<Envelope>
  <Body>
    <StockName>T</StockName>
    <StockName>N</StockName>
  </Body>
</Envelope>
"""

dom: minidom.Document = minidom.parseString(dummy_xml)
body: minidom.Element = dom.getElementsByTagName("Body")[0]

child_node: minidom.Node
for child_node in body.childNodes:
  inner_node: minidom.Node | None = child_node.firstChild
  if inner_node is not None:
    	print(inner_node.nodeValue)

The example above prints T and N as expected, but Pylance reports the following issue:

Cannot access member "nodeValue" for type "Node"
Member "nodeValue" is unknown - Pylance (reportGeneralTypeIssues)

Indeed the nodes we process happen to be Elements - therefore the attribute is defined at runtime. However during static analysis this is unknown despite this being legal according to the documentation.

Proposed solution

As far as i can tell this would be very easy to fix: just by initializing this attribute to None in the Node class (as is done for other similar attributes), this problem could be fully resolved:

cpython/Lib/xml/dom/minidom.py

Lines 34 to 40 in b99ac1d

    
           class Node(xml.dom.Node): 
        
               namespaceURI = None # this is non-null only for elements and attributes 
        
               parentNode = None 
        
               ownerDocument = None 
        
               nextSibling = None 
        
               previousSibling = None

While we're at it it'd be worth double checking if other attributes are affected by the same issue. I can submit a PR in a few hours if you'd like.

My environment

CPython versions tested on: 3.8.2, 3.10.8, 3.11.0
Operating system and architecture: RHEL7.9 x86_64, Windows 10 x86_64

The text was updated successfully, but these errors were encountered:

dylan-robins added the type-bug An unexpected behavior, bug, or error label Jan 3, 2023

mdboom added the expert-XML label Jan 3, 2023

[xml.dom.minidom] nodeValue attr is not defined on Node class but directly on all derived classes #100710

[xml.dom.minidom] nodeValue attr is not defined on Node class but directly on all derived classes #100710

Comments

dylan-robins commented Jan 3, 2023

[xml.dom.minidom] nodeValue attr is not defined on Node class but directly on all derived classes

Proposed solution

My environment