xlsx

| Task | Approach | |---|---| | **Create** or **edit** with formulas/formatting | `openpyxl` — see gotchas below | | **Bulk data** in or out | `pandas` (`read_excel`, `to_excel`) | | **Quick look** at a sheet | `markitdown file.xlsx` — `## SheetName` per sheet; reads `.xlsm` too. No cell coordinates, so don't plan edits from it | | **Read** a model (formulas *and* values) | two `load_workbook` passes — see gotchas | > `openpyxl`, `pandas`, and `markitdown` are preinstalled — do not run `pip install` first; write the script and import directly. Only if an import fails (or the `markitdown` command is missing): `pip install` the missing package. > Script paths below are relative to this skill's directory.

- **Professional font** (Arial, Times New Roman) throughout, unless the user says otherwise. - **Zero formula errors.** Never ship while `recalc.py` reports `errors_found`. If you think an error predates you, prove it: load the *original* with `data_only=True` and look at that cell. An error you introduced looks exactly like one you inherited. - **Use formulas, never hardcoded results.** Write `sheet['B10'] = '=SUM(B2:B9)'`, not the Python-computed total. The sheet must recalculate when its inputs change. - **Follow the user's spec literally.** Exact tab names, exact column headers, and the formula they spelled out. A redesign that computes something else fails, however elegant. - **Document every assumption and hardcoded number** where the reader will see it — a cell comment, or an adjacent cell at a table's end. Cite a real source when one exists (`Source: Company 10-K, FY2024, Page 45, Revenue Note, [SEC EDGAR URL]`); when the number came from the user, say so plainly. - **A workbook *you create* for someone to fill in** needs a short legend naming which cells to edit, and one example row of realistic values showing the expected format. Never add such a row to a file you were asked to edit. - **Editing an existing file: match its conventions exactly.** They override every guideline here. Find its designated input cells first — a distinct font color, fill, or shading marks them — write only there, and leave every existing formula untouched.

openpyxl writes formulas as strings with **no cached values**. Until you recalculate, every formula cell reads back as `None` to anything reading cached values — `pandas`, `load_workbook(data_only=True)`, and most previewers. ```bash python scripts/recalc.py output.xlsx [timeout_seconds] # default 30 ``` LibreOffice computes every formula, the file is **rewritten in place**, and you get JSON: `status` (`success` | `errors_found`), `total_formulas`, `total_errors`, and an `error_summary` naming up to 100 cells per error type (`locations_truncated` says how many it withheld — trust `total_errors`, not the length of the list). Fix what it names and run it again. **JSON with an `error` key instead of a `status` means nothing was recalculated**, and only that case exits non-zero — `errors_found` exits 0, so never treat a clean exit as a clean workbook. **A green recalc proves your formulas *evaluate*, not that they are *right*.** An off-by-one range or a reference to the wrong row yields a clean, error-free file with wrong numbers. Write 2–3 formulas first and check they pull the values you expect, before building out a grid. **A workbook that links to another file loses those links** if you re-save it with openpyxl and then recalculate. Such a formula reads `='[1]Returns Analysis'!$B$2` — the `[1]` is an index into the workbook's external-reference list, naming a *separate file on disk*, not a sheet. That file is rarely present here, so the cell's cached value is the only thing holding its data. openpyxl strips that value on save; LibreOffice then has to resolve the reference for real, fails, writes `#NAME?`, and deletes every link. `recalc.py` refuses to run in that state — copy those cells' values out of the original before you save over them (`--force` overrides, and accepts the loss).

LibreOffice implements fewer functions than Excel, and one it cannot evaluate becomes a literal `#NAME?` baked into the file you deliver. - **Prefer Excel-2007-era functions** — `SUMIFS`, `INDEX`, `MATCH`, `IFERROR`, `SUMPRODUCT` — which need no prefix. - **Six post-2007 functions work, but only with an `_xlfn.` prefix**, because openpyxl writes your formula into the XML verbatim and Excel stores post-2007 names prefixed (its UI hides the prefix): `_xlfn.TEXTJOIN`, `_xlfn.CONCAT`, `_xlfn.IFS`, `_xlfn.SWITCH`, `_xlfn.MAXIFS`, `_xlfn.MINIFS`. Written bare, each yields `#NAME?`. - **Never use `XLOOKUP`, `XMATCH`, `SORT`, `FILTER`, `UNIQUE`, or `SEQUENCE`.** The runtime's LibreOffice cannot evaluate them under *any* prefix. Newer builds do evaluate them, but they are spilling array functions and an openpyxl-written file has no spill metadata, so only the top-left cell of the range gets a value — and `recalc.py` reports `total_errors: 0` on the truncated result. Use `INDEX`/`MATCH` for lookups, and sort, filter, and de-duplicate in Python before writing the cells. - A formula LibreOffice could not parse is written back **lowercased** — a quick tell beside a `#NAME?`.

- **Reading a model takes two loads.** `data_only=True` yields cached values with the formulas gone; the default yields formula strings with no values. One pass cannot give you both. - **`data_only=True` is destructive if you save.** That workbook has no formulas left, so saving replaces every one with a literal — permanently. - **`data_only=True` on a file openpyxl just wrote returns `None` everywhere** — run `recalc.py` first. (A formula whose result is `""` also reads back as `None`.) - **Merged cells: write the top-left anchor only.** Every other cell in the range is a `MergedCell` whose `.value` is read-only. - **`.xlsm` loses its macros unless you pass `keep_vba=True`** to `load_workbook`. - **A sheet name containing a space must be quoted** in a cross-sheet reference: `='Assumptions Inputs'!$B$5`. Unquoted, it evaluates to `#VALUE!`.