openpyxl / python-docx / reportlab

Three libraries cover most Python document automation: openpyxl for Excel, python-docx for Word, and reportlab for PDF generation - common in reporting, exports, and compliance workflows.

Recipe

from openpyxl import Workbook
 
wb = Workbook()
ws = wb.active
ws.title = "Summary"
ws.append(["sku", "qty", "revenue"])
ws.append(["ABC", 10, 199.90])
wb.save("report.xlsx")

When to reach for this:

• Exporting query results to Excel for finance/ops
• Mail-merge style Word docs from CRM data
• Invoices, packing slips, and certificates as PDF
• Scheduled report jobs in Celery/cron

Working Example

from __future__ import annotations
 
from datetime import datetime, timezone
from io import BytesIO
 
from openpyxl import Workbook
from reportlab.lib.pagesizes import letter
from reportlab.pdfgen import canvas
 
 
def build_sales_xlsx(rows: list[tuple[str, int, float]]) -> bytes:
    wb = Workbook()
    ws = wb.active
    ws.title = "Sales"
    ws.append(["product", "units", "revenue"])
    for product, units, revenue in rows:
        ws.append([product, units, revenue])
    buf = BytesIO()
    wb.save(buf)
    return buf.getvalue()
 
 
def build_invoice_pdf(invoice_id: str, total: float) -> bytes:
    buf = BytesIO()
    c = canvas.Canvas(buf, pagesize=letter)
    c.setFont("Helvetica", 12)
    c.drawString(72, 720, f"Invoice {invoice_id}")
    c.drawString(72, 700, f"Total: ${total:,.2f}")
    c.drawString(72, 680, datetime.now(timezone.utc).isoformat())
    c.showPage()
    c.save()
    return buf.getvalue()
 
 
if __name__ == "__main__":
    xlsx = build_sales_xlsx([("widget", 3, 59.97)])
    pdf = build_invoice_pdf("INV-1001", 59.97)
    print(len(xlsx), len(pdf))

What this demonstrates:

• In-memory workbooks via BytesIO for HTTP responses
• Simple tabular xlsx without pandas overhead
• Minimal PDF with reportlab canvas API
• UTC timestamp on PDF for audit trail

Deep Dive

How It Works

• openpyxl - OOXML xlsx; load_workbook for edits; data_only=True reads cached formula values.
• python-docx - Manipulates WordprocessingML; paragraphs, tables, styles; template merge by replacing placeholders.
• reportlab - Low-level PDF canvas plus Platypus flowables for complex layouts.

Library Picker

Python Notes

from docx import Document
 
doc = Document("template.docx")
for p in doc.paragraphs:
    if "{{NAME}}" in p.text:
        p.text = p.text.replace("{{NAME}}", "Ada Lovelace")
buf = BytesIO()
doc.save(buf)

Gotchas

• Loading untrusted xlsx - XML bombs and billion-laughs variants exist. Fix: size limits, virus scan, parse in sandbox worker.
• Formulas vs values - load_workbook returns formulas by default. Fix: data_only=True for displayed values (stale until Excel opens).
• python-docx unsupported features - Headers/footers in complex templates may break. Fix: simplify template or use docx templates maintained in Word.
• reportlab font licensing - Embed only licensed fonts for commercial PDFs. Fix: use built-in Helvetica or licensed TTF.
• Memory on huge exports - Building million-row xlsx in RAM OOMs. Fix: CSV for big data, or chunked writes with write_only=True mode.
• Locale and dates in Excel - Excel displays local format; store ISO in source data. Fix: explicit number formats in openpyxl.

Alternatives

FAQs

Related

• pandas Basics - DataFrame to Excel
• celery - async report generation
• S3 - storing generated documents
• pendulum / arrow - dates in reports

Stack versions: This page was written for Python 3.14.0 (stable 3.14, maintenance 3.13), FastAPI 0.115+, Django 5.2, Flask 3.1, Pydantic 2, PyTorch 2.6+, pandas 2.2+, Polars 1.x, ruff 0.9+, and uv 0.6+.