Excel Builder

Builds structured .xlsx files programmatically using Python libraries (openpyxl or xlsxwriter).

When to Use This Skill

• Creating Excel spreadsheets with formulas and calculated fields
• Building financial tables, budgets, or invoices
• Generating data entry forms with validation and dropdowns
• Producing reports with charts (bar, line, pie, scatter)
• Exporting structured data with conditional formatting or color coding
• Building pivot-ready data tables

Core Workflow

1. Choose library — Use openpyxl for reading/modifying existing files; use xlsxwriter for new write-only files with rich charts
2. Design structure — Define sheets, columns, headers, and data rows before writing
3. Write data — Populate cells row by row; apply number formats ("#,##0.00", "YYYY-MM-DD")
4. Add formulas — Use Excel formula strings: =SUM(B2:B100), =IF(A2>0, "Yes", "No")
5. Format — Apply styles: bold headers, column widths, merged cells, fill colors, borders
6. Validate — Add data validation (dropdown lists, numeric ranges) where applicable
7. Charts — Add charts referencing data ranges; set titles and axis labels
8. Save and verify — Save to output path; confirm file exists and is non-zero bytes

Key Patterns

openpyxl (read/write existing)

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

wb = Workbook()
ws = wb.active
ws.title = "Report"
ws["A1"] = "Revenue"
ws["A1"].font = Font(bold=True, size=12)
ws.column_dimensions["A"].width = 20
wb.save("output.xlsx")

xlsxwriter (new files with charts)

import xlsxwriter
wb = xlsxwriter.Workbook("output.xlsx")
ws = wb.add_worksheet("Summary")
bold = wb.add_format({"bold": True, "bg_color": "#4472C4", "font_color": "white"})
ws.write("A1", "Month", bold)
chart = wb.add_chart({"type": "column"})
chart.add_series({"values": "=Summary!$B$2:$B$13", "name": "Revenue"})
ws.insert_chart("D2", chart)
wb.close()

Error Handling

• If openpyxl not installed: pip install openpyxl
• If xlsxwriter not installed: pip install xlsxwriter
• Always wrap wb.save() in try/except; report path conflicts
• Verify output with os.path.getsize(path) > 0 before returning

Output

Return the absolute path to the saved .xlsx file. If generating multiple sheets, list each sheet name and row count in a brief summary.