xtl-py 0.1.0a3

XTL (Excel Template Language) 0.1 — Python reference implementation

xtl-py

A Python reference implementation of XTL (Excel Template Language) 0.1 — a host-language–agnostic templating language that turns an .xlsx template plus an .xlsx data workbook into one or more rendered output workbooks.

xtl-py is the second implementation of the language, built alongside the TypeScript reference impl as portability validation: if both implementations produce identical output for the same conformance corpus, the spec is real.

• Spec & TS reference: https://github.com/jinyoung4478/xl3 (XTL spec 0.1.0 released 2026-05-08).
• Conformance status (xl3 0.7.0 corpus): 133 / 133 stage-1 fixtures passing (100%) — 6 stage-2 fixtures skipped (canonical OOXML comparison out of scope for v0.1). The 5 spec/impl ambiguities found while building this port were filed as xl3 issue #1 and resolved upstream the same day; see PORTING_NOTES.md for the full sync log (0.5 → 0.6 → 0.7).

Install

pip install xtl-py

⚠️ The PyPI distribution name is xtl-py but the import name is xl3 (matching the TS package on npm).

from xl3 import convert  # NOT `import xtl_py`

Requires Python ≥ 3.11.

Quick start

from xl3 import convert

with open("template.xlsx", "rb") as f:
    template = f.read()
with open("data.xlsx", "rb") as f:
    data = f.read()

output_files = convert(template, data)

for f in output_files:
    with open(f.filename, "wb") as out:
        out.write(f.data)
    print("wrote", f.filename)

Runtime inputs (ADR-0010)

from xl3 import convert, ConvertOptions

output = convert(
    template,
    data,
    ConvertOptions(inputs={"month": "2026-05", "region": "Seoul"}),
)

Inspecting a template

from xl3 import preview, read_template_inputs

# Lightweight: returns parsed file/sheet/row counts + warnings without rendering.
result = preview(template, data)

# Just the input declarations (for building a host UI).
specs = read_template_inputs(template)

Structured errors

from xl3 import convert, is_xtl_error

try:
    convert(template, data)
except Exception as e:
    if is_xtl_error(e):
        print(e.code, e)  # e.g. "xl3/source/sheet-missing", message
    else:
        raise

Every spec-defined error carries a stable xl3/<category>/<id> code per ADR-0015. The English message is the conformance contract; hosts should dispatch on code.

Conformance runner

The package ships a CLI runner that implements conformance/runner-protocol.md:

# Full stage-1 run against an xl3 fixture directory
python -m xl3.runner --fixture-dir /path/to/xl3/conformance/fixtures

# JSON report
python -m xl3.runner --report json

# Filter
python -m xl3.runner --filter substitution
python -m xl3.runner --id-prefix 050

Output sample:

xl3-py 0.1.0a3 — XTL 0.1 (stage 1)
  pass   001-bracket-substitution
  pass   002-if-function
  ...
summary: 133/133 passed, 0 failed, 6 skipped

What is supported

Surface	Status
Bracket substitution {{ [Col] }}	✅
IF / IFEMPTY / ROUND / ABS / TEXT / TODAY / ROW	✅
Aggregates SUM / COUNT / AVERAGE / MIN / MAX	✅
XLOOKUP (3-arg + 4-arg)	✅
Directives @filter / @sort / @top / @repeat right / @source / @join	✅
__config__ / __inputs__ / __sources__ / __lists__ reserved sheets	✅
ADR-0007 / 0008 / 0009 / 0017 value model	✅ (82 unit tests pinning the contract)
ADR-0002 filename sanitization	✅
ADR-0003 numFmt-driven coercion	✅
ADR-0010 runtime inputs (text / number / date / select)	✅
ADR-0012 multi-source data model	✅
ADR-0013 XLOOKUP cross-source	✅
ADR-0014 single inner @join	✅
ADR-0016 file/sheet group splitting (first-seen order)	✅
Stage-2 canonical OOXML comparison	❌ (out of scope for v0.1; deferred)

Architecture

Pure-Python, sync API, single dependency on openpyxl for Excel I/O.

src/xl3/
├── __init__.py        # public API
├── errors.py          # XtlError + ADR-0015 stable code catalog
├── value_model.py     # is_empty / is_truthy / canonical_string /
│                      # canonical_number / compare_values
├── expression.py      # cell-template lexer + recursive-descent parser
├── evaluator.py       # AST eval + ROW / aggregates / XLOOKUP
├── functions.py       # IF / IFEMPTY / ROUND / ABS / TEXT / TODAY
├── directives.py      # @filter / @sort / @top / @repeat / @source / @join
│                      # + row-set transform pipeline
├── inputs.py          # ADR-0010 input resolution
├── filename.py        # ADR-0002 sanitization
├── parser.py          # template workbook → block plan
├── reader.py          # source workbook reader (multi-source)
├── renderer.py        # block-based renderer with file/sheet groups
├── pipeline.py        # convert / preview / read_template_inputs
└── runner/            # conformance runner CLI

Status

Pre-1.0 / alpha. API surface mirrors the TS reference. Breaking changes are possible until the spec freezes at XTL 1.0; see spec/STABILITY.md in the spec repo.

License

MIT — see the spec repo's LICENSE.