Live-Formula Excel Model (Operate)

Overview

Finance professionals ultimately want a workbook where changing an assumption recalculates the model. This skill produces one from the model structure, with named assumption cells and real formulas, then proves it reproduces the engine before it ships. Static value dumps stay with forecast_to_excel; this skill is for living models.

Core principle: no workbook ships unverified. The workbook is generated from the model, never hand-edited values.

The standard model

For the kernel's monthly model, one call:

import pyfpa
cfg = pyfpa.load_config("config.yaml")
pyfpa.model_to_excel(cfg, "model.xlsx")

Or via CLI: python3 -m pyfpa.cli model-export <company-root> --config config.yaml --out model.xlsx.

The workbook has an Assumptions sheet (every driver a named, editable cell: growth, COGS pct, seasonality, DSO/DIO/DPO, debt, tax, D&A, capex) and a Model sheet where every line of the monthly P&L and cash flow is a formula referencing those names.

Any other cadence or layout

Quarterly, weekly, a tab per segment, a lender view: these are YOUR work, not kernel variants. Compose pyfpa.excel.toolkit (add_named_cell, add_named_row, fill_formula_row, formats) in a company-specific exporter under the generated namespace (models/generated/<name>/), then register it:

python3 -m pyfpa.cli entrypoint-register <root> --name excel-quarterly --kind report \
  --description "Quarterly live-formula workbook" \
  --command-json '["python3", "models/generated/<name>/excel_quarterly.py"]'

Keep formulas within the supported vocabulary (arithmetic, ^, SUM, MIN, MAX, IF) so verification works.

Verify before delivering (always)

1. pip install formulas (verification-only dependency, not shipped at runtime).
2. ```python

report = pyfpa.verify_workbook("model.xlsx", pyfpa.cashflow_from_config(cfg)) assert report.passed, report.failures

3. For a bespoke exporter, verify against the frame your exporter is meant to
   reproduce (the engine frame, or its quarterly/weekly aggregation).
4. A failing report means the exporter is wrong. Fix the formulas, never the
   tolerance, and never deliver an unverified workbook.

## Guardrails

- No workbook ships unverified.
- Generated from model structure; never paste computed values into formula cells.
- Supported formula vocabulary only; if you need a function outside it, restructure
  the formula (helper rows are fine) rather than expanding the vocabulary.
- Company-specific exporters live in generated namespaces and get tests like any
  other generated code.

## Next

Workbook delivered, then **fpa-board-briefing** (the narrative that goes with it).