<!-- Adapted from: awesome-claude-skills/document-skills/xlsx -->

Excel/Spreadsheet Processing Guide

Create, edit, and analyze spreadsheets with formulas and formatting.

Library Selection

Task	Best Tool
Data analysis	pandas
Formulas & formatting	openpyxl
Simple CSV	pandas
Financial models	openpyxl

Reading Data with Pandas

import pandas as pd

# Read Excel
df = pd.read_excel('file.xlsx')  # First sheet
all_sheets = pd.read_excel('file.xlsx', sheet_name=None)  # All sheets

# Analyze
df.head()       # Preview
df.info()       # Column info
df.describe()   # Statistics

# Write
df.to_excel('output.xlsx', index=False)

Creating with openpyxl

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

wb = Workbook()
sheet = wb.active

# Add data
sheet['A1'] = 'Revenue'
sheet['B1'] = 1000
sheet.append(['Q1', 'Q2', 'Q3', 'Q4'])

# Add formula (NEVER hardcode calculations!)
sheet['B5'] = '=SUM(B1:B4)'

# Formatting
sheet['A1'].font = Font(bold=True)
sheet['A1'].fill = PatternFill('solid', fgColor='FFFF00')
sheet.column_dimensions['A'].width = 15

wb.save('output.xlsx')

Critical: Use Formulas, Not Hardcoded Values

# ❌ WRONG - Hardcoding
total = df['Sales'].sum()
sheet['B10'] = total  # Hardcodes 5000

# ✅ CORRECT - Excel formula
sheet['B10'] = '=SUM(B2:B9)'

Editing Existing Files

from openpyxl import load_workbook

wb = load_workbook('existing.xlsx')
sheet = wb.active

# Modify
sheet['A1'] = 'New Value'
sheet.insert_rows(2)
sheet.delete_cols(3)

# Add sheet
new_sheet = wb.create_sheet('NewSheet')

wb.save('modified.xlsx')

Financial Model Standards

Color Coding

Color	Use
Blue text	Hardcoded inputs
Black text	Formulas
Green text	Links to other sheets
Yellow fill	Needs attention

Number Formats

# Currency
sheet['A1'].number_format = '$#,##0'

# Percentage
sheet['B1'].number_format = '0.0%'

# Negative in parentheses
sheet['C1'].number_format = '#,##0;(#,##0)'

Common Formula Errors

Error	Cause	Fix
#REF!	Invalid reference	Check cell exists
#DIV/0!	Division by zero	Add IF check
#VALUE!	Wrong data type	Verify inputs
#NAME?	Unknown function	Check spelling

Best Practices

1. Always use formulas - Never hardcode calculations
2. Document sources - Comment cells with data sources
3. Test formulas - Verify with sample data first
4. Preserve formatting - Use load_workbook() not pandas for edits
5. Handle data_only carefully - Using data_only=True loses formulas on save

Required Packages

pip install pandas openpyxl xlrd