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Label Printers

Authors:
Geoffrey Hunter
Geoffrey Hunter
Published On:
May 19, 2025
Last Updated:
May 19, 2025

Label printers are useful in electronics work for labelling PCBs, cables, production items and more.

Printing From Python in Windows

The pywin32 Python library can be used to print to most label printers on Windows. This library makes it easy to interact with the Win32 API, which includes printer operations. You can install it using pip:

Terminal window
pip install pywin32

Here is an example of how to print a image to the label printer using the pywin32 library. In this case I was connected to a Brady M511 label printer.

import datetime
import os
import sys


from PIL import Image, ImageWin
import win32con
import win32print
import win32ui


file_name = os.path.join(SCRIPT_DIR, "test.png")
# Create device context
hDC = win32ui.CreateDC()
hDC.CreatePrinterDC(printer_name)


# Get printer dimensions in device units
printer_width = hDC.GetDeviceCaps(win32con.PHYSICALWIDTH)
printer_height = hDC.GetDeviceCaps(win32con.PHYSICALHEIGHT)


# Open and prepare the image
bmp = Image.open(file_name)


# Calculate scaling factor to fit the image within printer dimensions
# while maintaining aspect ratio
width_ratio = printer_width / bmp.size[0]
height_ratio = printer_height / bmp.size[1]
scale_factor = min(width_ratio, height_ratio)


# Calculate new dimensions
new_width = int(bmp.size[0] * scale_factor)
new_height = int(bmp.size[1] * scale_factor)


# Resize the image
bmp = bmp.resize((new_width, new_height), Image.Resampling.LANCZOS)


# Calculate centering offsets
x_offset = (printer_width - new_width) // 2
y_offset = (printer_height - new_height) // 2


# Start printing
hDC.StartDoc(file_name)
hDC.StartPage()


# Draw the image centered on the page
dib = ImageWin.Dib(bmp)
dib.draw(hDC.GetHandleOutput(), (0, 0, new_width, new_height))


hDC.EndPage()
hDC.EndDoc()
hDC.DeleteDC()

GetDeviceCaps() can be used to retrieve a number of different properties of the printer. Some of the things you can request are:

  • HORZRES: Printable area width in pixels
  • VERTRES: Printable area height in pixels
  • LOGPIXELS: Dots per inch
  • PHYSICALWIDTH: Total area width in device units
  • PHYSICALHEIGHT: Total area height in device units
  • PHYSICALOFFSETX: Left margin in device units
  • PHYSICALOFFSETY: Top margin in device units
These constants are defined in the `win32con.py` file as part of the `pywin32` library.


```python
import win32con


print(win32con.PHYSICALWIDTH)

If you are wanting to change the label size, you need to set the paper width and length attributes. To do this, you need to open the printer with the ACCESS_MASK set to win32print.PRINTER_ALL_ACCESS:

PRINTER_DEFAULTS = {"DesiredAccess": win32print.PRINTER_ALL_ACCESS}
printer_handle = win32print.OpenPrinter(printer_name, PRINTER_DEFAULTS)

Here is an example which set a number of different attributes for a printer.

# PRINTER_ALL_ACCESS is required to set paper size
PRINTER_DEFAULTS = {"DesiredAccess": win32print.PRINTER_ALL_ACCESS}
printer_handle = win32print.OpenPrinter(printer_name, PRINTER_DEFAULTS)


# 2 : A PRINTER_INFO_2 structure containing detailed information about the printer.
# See https://learn.microsoft.com/en-us/windows/win32/printdocs/setprinter
level = 2
attributes = win32print.GetPrinter(printer_handle, level)
# Width is perpendicular to the label feed direction
# Length is parallel with the label feed direction
# Both of these are in tenths of a millimeter
attributes['pDevMode'].PaperWidth = 90
attributes['pDevMode'].PaperLength = 80


# For printer devices only, selects the size of the paper to print on.
# This member can be set to zero if the length and width of the paper are
# both set by the dmPaperLength and dmPaperWidth members
# (https://learn.microsoft.com/en-us/windows/win32/api/wingdi/ns-wingdi-devmodea)
attributes['pDevMode'].PaperSize = 0


# Print 2 copies of the label
attributes['pDevMode'].Copies = 2


win32print.SetPrinter(printer_handle, level, attributes, 0)

I have found that setting changing the printer length can change the position a label is cut on a continuous cartridge.

Be careful when changing the printer paper size. As fair I have found, this will apply the new paper size to all pending print jobs, including ones you have previously submitted but have not yet been printed.

This code example also uses Copies to set the number of copies to print. I found this to be more reliable than submitting the print job multiple times.

Detecting If A Printer Is Connected

It can be useful to be able to detect if a printer is connected and ready to print. If you don’t check this, your printing efforts could just end up queuing up a load of print jobs but not actually printing anything. This is not ideal in a production line environment.

The GetPrinter(<printer_handle>, 2) function can be used to get printer information. I would have thought the status field would have been the variable to check, but in my testing it was always 0, whether the printer was actually connected or not. Instead I used the PRINTER_ATTRIBUTE_WORK_OFFLINE attribute. This seems to be set to 1024 when the printer is not connected, and 0 when it is.

Below is an example function which returns True if the printer is connected (online).

def is_printer_connected(printer_name: str) -> bool:
    """
    Checks if the specified printer is connected and ready to print.


    Args:
        printer_name (str): The name of the printer to check.


    Returns:
        bool: True if the printer is connected and ready, False otherwise.
    """
    try:
        # Check if printer exists in the list of available printers
        available_printers = list_windows_printers()
        if printer_name not in available_printers:
            print(f"Printer '{printer_name}' not found in available printers")
            return False


        # Try to open the printer to check if it's accessible
        PRINTER_DEFAULTS = {"DesiredAccess": win32print.PRINTER_ACCESS_USE}
        printer_handle = win32print.OpenPrinter(printer_name, PRINTER_DEFAULTS)


        if printer_handle:
            # Get printer status
            level = 2
            printer_info = win32print.GetPrinter(printer_handle, level)
            attributes = printer_info['Attributes']
            # Status did not change from 0, so we are using this WORK_OFFLINE attribute instead.
            # Is seems to be set to 1024 when not connected, and 0 when connected.
            is_ready = (attributes & win32print.PRINTER_ATTRIBUTE_WORK_OFFLINE) == 0
            win32print.ClosePrinter(printer_handle)
            return is_ready
    except Exception as e:
        print(f"Error checking printer status: {e}.")
        return False
    return False