Spreadsheet Files

Overview

Use this skill whenever the primary deliverable is a spreadsheet file or the user explicitly wants work done on spreadsheet data in place. Prefer openpyxl when workbook structure, formulas, styling, or multiple sheets must be preserved. Use pandas for analysis and reshaping, then write the final workbook carefully instead of treating the spreadsheet as a disposable export.

Non-Negotiable Rules

• Use formulas in the workbook instead of calculating values in Python and hardcoding the result.
• Preserve existing workbook structure unless the user asked for destructive cleanup.
• Recalculate and verify formulas after edits with scripts/recalc.py.
• Keep formatting readable: sensible column widths, aligned headers, and explicit number formats.
• If editing a financial model, keep assumptions visually distinct from formulas and outputs.

Choose the Workflow

Existing workbook

Use openpyxl when the file already exists and you must preserve:

• formulas,
• formatting,
• named sheets,
• comments,
• workbook-level structure.

New workbook or pure analysis

Use pandas for:

• data cleaning,
• joins,
• aggregation,
• reshaping.

Then write the final spreadsheet with either:

• pandas if a simple flat export is enough, or
• openpyxl if formulas, formatting, or multiple sheets matter.

Core Workflow

1. Inspect the workbook or source data.
2. Decide whether the task is analysis-only, structure-preserving edit, or workbook creation.
3. Make the edits.
4. Recalculate formulas with python scripts/recalc.py <excel_file>.
5. Fix any reported workbook errors before handoff.

Reading and Analyzing Data

Pandas quick read

import pandas as pd

df = pd.read_excel("file.xlsx")
all_sheets = pd.read_excel("file.xlsx", sheet_name=None)

print(df.head())
print(df.info())
print(df.describe(include="all"))

Openpyxl structure-preserving read

from openpyxl import load_workbook

wb = load_workbook("existing.xlsx")
print(wb.sheetnames)

ws = wb["Sheet1"]
print(ws["A1"].value)

Use Formulas, Not Hardcoded Values

Wrong

total = df["Sales"].sum()
sheet["B10"] = total

Correct

sheet["B10"] = "=SUM(B2:B9)"
sheet["C5"] = "=(C4-C2)/C2"
sheet["D20"] = "=AVERAGE(D2:D19)"

This rule applies to totals, percentages, growth rates, averages, ratios, and derived metrics in general.

Creating a New Workbook

from openpyxl import Workbook
from openpyxl.styles import Font, PatternFill, Alignment

wb = Workbook()
ws = wb.active
ws.title = "Summary"

ws["A1"] = "Metric"
ws["B1"] = "Value"
ws["A2"] = "Revenue"
ws["B2"] = 125000
ws["A3"] = "Cost"
ws["B3"] = 83000
ws["A4"] = "Profit"
ws["B4"] = "=B2-B3"

header_fill = PatternFill("solid", start_color="D9EAF7")
for cell in ws[1]:
    cell.font = Font(bold=True)
    cell.fill = header_fill
    cell.alignment = Alignment(horizontal="center")

ws.column_dimensions["A"].width = 18
ws.column_dimensions["B"].width = 14

wb.save("output.xlsx")

Editing an Existing Workbook

from openpyxl import load_workbook

wb = load_workbook("existing.xlsx")
ws = wb["Sheet1"]

ws["A1"] = "New Value"
ws.insert_rows(2)
ws.delete_cols(3)

new_sheet = wb.create_sheet("NewSheet")
new_sheet["A1"] = "Data"

wb.save("modified.xlsx")

Recalculate and Verify

After editing any workbook with formulas, run:

python scripts/recalc.py output.xlsx

Optional timeout override:

python scripts/recalc.py output.xlsx 30

The script:

• sets up LibreOffice automation when needed,
• recalculates formulas,
• scans all sheets for Excel errors,
• returns JSON with counts and cell locations.

Example output

{
  "status": "success",
  "total_errors": 0,
  "total_formulas": 42
}

If errors are reported

Typical fixes:

• #REF!: invalid references after row or column edits.
• #DIV/0!: denominator can be zero.
• #VALUE!: wrong data type in a formula input.
• #NAME?: misspelled function or unsupported name.

Do not hand off the workbook until recalculation is clean or the user explicitly accepts the remaining issues.

Financial Model Conventions

When the workbook behaves like a model rather than a data dump:

• keep assumptions in dedicated cells or sheets,
• label units and time periods explicitly,
• apply consistent number formats,
• visually separate inputs, formulas, and outputs,
• add comments for non-obvious hardcoded assumptions.

Verification Checklist

• Workbook opens successfully.
• Expected sheets are present.
• Key formulas still point at the right ranges.
• Number formats and percentages are readable.
• No accidental hardcoded replacements were introduced.
• scripts/recalc.py reports success or the remaining issues are documented.

Notes

• Use openpyxl for workbook fidelity.
• Use pandas for tabular transformation.
• Use local scripts in scripts/ instead of rebuilding recalculation helpers ad hoc.