Pyodide Quickstart

Formualizer publishes a Pyodide-tagged wheel (*-pyodide_<abi>_wasm32.whl) alongside the native CPython wheels. Any Python code that works against formualizer on CPython works the same inside a Pyodide runtime — with a few platform-specific defaults noted below.

1) Install in a Pyodide runtime

import micropip
await micropip.install("formualizer")

This resolves the Pyodide-tagged wheel from PyPI — no extra index URL, no manual wheel download.

2) Evaluate a formula

import formualizer as fz

wb = fz.Workbook()
wb.add_sheet("Sheet1")

wb.set_value("Sheet1", 1, 1, 100)
wb.set_value("Sheet1", 2, 1, 20)
wb.set_formula("Sheet1", 1, 2, "=A1-A2")

result = wb.evaluate_cell("Sheet1", 1, 2)
print(result)  # 80.0

3) Register a Python UDF

wb.register_function(
    "py_add",
    lambda a, b: a + b,
    min_args=2,
    max_args=2,
)
wb.set_value("Sheet1", 1, 1, 20)
wb.set_value("Sheet1", 2, 1, 22)
wb.set_formula("Sheet1", 1, 2, "=PY_ADD(A1, A2)")
wb.evaluate_cell("Sheet1", 1, 2)  # 42

Single-cell references arrive as scalars in the callback, matching Excel semantics.

4) Round-trip an XLSX file

xlsx_bytes = wb.to_xlsx_bytes()
# ... send to browser download, IndexedDB, fetch upload, etc.

restored = fz.load_workbook_bytes(xlsx_bytes)
restored.evaluate_cell("Sheet1", 1, 2)

Supported Pyodide versions

The published wheel targets Pyodide 0.29.x (ABI pyodide_2025_0). Check the formualizer release that matches your Pyodide runtime — when Pyodide ships a new ABI, a new formualizer release is cut against it.

Pyodide-specific behavior

• EvaluationConfig() and Workbook() default enable_parallel = False on sys.platform == "emscripten". Pyodide has no threads; the flag remains available but falls back to single-threaded execution.
• XLSX byte I/O (to_xlsx_bytes, from_bytes, load_workbook_bytes) uses the umya backend on all platforms.
• Everything else — parse, evaluate, spill, custom functions, undo/redo, SheetPort — behaves identically to native CPython.

Next

• Python Quickstart — the same API on native CPython
• First Workbook in 5 Minutes
• Custom Functions (Rust, Python, JS)