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Batch label printer

Super simple FastAPI app to print ZPL labels in batches to a Zebra network printer.

What it does

  • Serves a single HTML form at http://localhost:8000/
  • Takes a SKU, batch number, and quantity
  • Generates a ZPL label (SKU text + Code-128 barcode + batch number)
  • Sends the label to a Zebra printer over TCP (raw port 9100)
  • Previews the label using the Labelary API

Stack

  • FastAPI — web framework
  • httpx — async HTTP client for Labelary preview
  • uvicorn — ASGI server
  • Raw ZPL strings (no external ZPL library)

Key files

  • main.py — entire app (ZPL generation, printer comms, HTML, routes)
  • test_main.py — integration tests (mock printer + Labelary)
  • pyproject.toml — dependencies

Config

All constants are read from environment variables (.env supported). Defaults are set at the top of main.py.

Printer

Constant Default Description
PRINTER_HOST 192.168.1.100 Printer IP address
PRINTER_PORT 9100 RAW TCP port (Zebra standard)

Label dimensions

Constant Default Description
LABEL_WIDTH 2.76 Label width in inches (70 mm)
LABEL_HEIGHT 1.42 Label height in inches (36 mm)
LABEL_DPI 203 Printer DPI (GK420D = 203)

Fonts

ZPL built-in fonts: 0=scalable (any size), A=9 pt, B=11 pt, D=18 pt, E=28 pt, F=26 pt bold, G=60 pt, H=21 pt bold

Constant Default Description
SKU_LABEL_FONT G ZPL font for SKU text
BATCH_LABEL_FONT 1 ZPL font for batch text

Text size (mm)

Constant Default Description
SKU_CHAR_HEIGHT 18 SKU character height (mm)
SKU_CHAR_WIDTH 12 SKU character width (mm)
BATCH_CHAR_HEIGHT 7 Batch character height (mm)
BATCH_CHAR_WIDTH 4 Batch character width (mm)

Padding (mm)

Constant Default Description
SKU_PADDING_LEFT 5 SKU distance from left edge (mm)
SKU_PADDING_TOP 5 SKU distance from top edge (mm)
BATCH_PADDING_BOTTOM 6 Batch distance from bottom edge (mm)
BATCH_PADDING_RIGHT 5 Batch distance from right edge (mm)

Running

uv run uvicorn main:app --reload

Testing

uv run pytest

Linting

uv run ruff check . --fix