# XLSX To Python Core Principle Excel Values Test Data

> Sub-skill of xlsx-to-python: Core Principle: Excel Values = Test Data.

- Skill: `vamseeachanta/xlsx-to-python-core-principle-excel-values-test-data` (Agent Skill)
- Install (CLI): `npx skillmds@latest add vamseeachanta/xlsx-to-python-core-principle-excel-values-test-data`
- Raw SKILL.md: https://api.skillmd.com/api/skills/vamseeachanta/xlsx-to-python-core-principle-excel-values-test-data/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Data & Analytics
- Author: vamseeachanta (https://skillmd.com/u/vamseeachanta)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/vamseeachanta/xlsx-to-python-core-principle-excel-values-test-data

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# Core Principle: Excel Values = Test Data

## Core Principle: Excel Values = Test Data


When an Excel spreadsheet contains a calculation with input values and computed
results, **those cell values are the test cases**. The two-pass extraction strategy:

- **Pass 1** (`data_only=True`): read computed cell values — these become `pytest.approx()` assertions
- **Pass 2** (`data_only=False`): read formula strings — these become Python function implementations

This means every spreadsheet with formulas is simultaneously a specification,
an implementation reference, AND a test fixture.