lvxml

Read and write LabVIEW's Flatten To XML data from Python, with no LabVIEW running. Typed, zero dependencies, Python 3.10 to 3.14.

The problem

LabVIEW's Flatten To XML and its file writer turn any LabVIEW value into one fixed XML shape: an element named after the data type (DBL, I32, Boolean, String, Cluster, Array, EW, ...) holding a <Name> and a <Val>, or for containers their sizes and children, usually inside an <LVData> file. A generic XML library parses the elements but knows none of the conventions, and LabVIEW's reader has its own rules: it decodes only three entities, writes control characters raw, puts a refnum's kind before its value and writes files in the system code page. lvxml follows what LabVIEW 2026 actually writes and reads, checked against files it wrote and values it read back.

Install

pip install lvxml

Quick start

>>> from lvxml import Array, Cluster, LVEnum, from_lv_xml, to_lv_xml
>>> from_lv_xml("<I32><Name>count</Name><Val>-7</Val></I32>")
-7
>>> from_lv_xml(
...     "<Cluster><Name>pt</Name><NumElts>2</NumElts>"
...     "<DBL><Name>x</Name><Val>1.5</Val></DBL>"
...     "<EW><Name>mode</Name><Choice>Idle</Choice><Choice>Run</Choice><Val>1</Val></EW>"
...     "</Cluster>"
... )
{'x': 1.5, 'mode': 'Run'}
>>> schema = Cluster({"x": "DBL", "mode": LVEnum(("Idle", "Run"))})
>>> print(to_lv_xml({"x": 1.5, "mode": "Run"}, schema, name="pt"))
<Cluster>
  <Name>pt</Name>
  <NumElts>2</NumElts>
  <DBL>
    <Name>x</Name>
    <Val>1.5</Val>
  </DBL>
  <EW>
    <Name>mode</Name>
    <Choice>Idle</Choice>
    <Choice>Run</Choice>
    <Val>1</Val>
  </EW>
</Cluster>

A file LabVIEW wrote is read as text in its code page and comes back byte for byte:

>>> from lvxml import dump, parse
>>> text = (
...     "<?xml version='1.0' standalone='yes' ?>\r\n<LVData xmlns=\"http://www.ni.com/LVData\">\r\n"
...     "<Version>26.3.1f1</Version>\r\n<Boolean>\r\n<Name>on</Name>\r\n<Val>1</Val>\r\n</Boolean>\r\n"
...     "</LVData>"
... )
>>> document = parse(text)
>>> document.version, document.values[0].val
('26.3.1f1', '1')
>>> dump(document) == text
True

The command line converts to and from JSON and validates files:

lvxml to-json --encoding cp1252 data.xml -o data.json
lvxml to-xml --encoding cp1252 data.json -o data.xml
lvxml validate data.xml

The guide covers every type, the typed tree, validation, errors, the command line and the evidence behind each rule. Changes are listed in the changelog.

Why

LabVIEW reads and writes this format natively, but only inside LabVIEW. On the Python side, the LabVIEW packages on PyPI work on other things: pylabview parses LabVIEW's binary file types, lvkit reads VIs and converts them to Python, and autolv drives a running LabVIEW. None of them turns this XML into Python values or writes XML that LabVIEW will read back, so that glue is usually written by hand around a generic XML parser, which gets entities, control characters and the code page wrong for real LabVIEW files. lvxml is that glue, small, typed and dependency free, tested against what LabVIEW 2026 itself writes and reads.

License

MIT. See the license.

Links

• Website: https://lianes8studio.com
• GitHub: https://github.com/JaviLianes8
• LinkedIn: https://www.linkedin.com/in/jlianes/