Robust Linux Python serial port filtering by name and manufacturer using udev

Important note: This code is deprecated as it has been superseded by the UliSerial library on GitHub. UIiSerial implements the serial port filtering in a platform-independent manner using pyserial built-in features.

Typically, when one intends to select a serial port in Python, you use a sequence such as

glob.glob('/dev/ttyACM*')[0]

or just go to straight hard-coding the port such as /dev/ttyACM0.

It should be quite obvious why this isn’t robust:

• There might be multiple serial ports and the order is unknown
• You code might need to work on different computers, which lead to different ports being assigned
• When you re-plug a device, it might get assigned a differnent serial port number (e.g. /dev/ttyACM1)

The following code uses only the linux integrated tool udevadm to query information and built-in libraries. Currently it does not work on anything but Linux.

import glob
import subprocess
import re

def get_serial_ports():
    # Get a list of /dev/ttyACM* and /dev/ttyUSB* devices
    ports = glob.glob('/dev/ttyACM*') + glob.glob('/dev/ttyUSB*')
    return ports

def get_udev_info(port):
    # Run the udevadm command and get the output
    result = subprocess.run(['udevadm', 'info', '-q', 'all', '-r', '-n', port], capture_output=True, text=True)
    return result.stdout

def find_serial_ports(vendor=None, model=None, usb_vendor=None, usb_model=None, usb_model_id=None, vendor_id=None):
    # Mapping of human-readable names to udevadm keys
    attribute_mapping = {
        "vendor": "ID_VENDOR_FROM_DATABASE",
        "model": "ID_MODEL_FROM_DATABASE",
        "usb_vendor": "ID_USB_VENDOR",
        "usb_model": "ID_USB_MODEL_ENC",
        "usb_model_id": "ID_USB_MODEL_ID",
        "vendor_id": "ID_VENDOR_ID",
        "usb_path": "ID_PATH",
        "serial": "ID_SERIAL_SHORT"
    }

    # Filters based on provided arguments
    filters = {}
    for key, value in locals().items():
        if value and key in attribute_mapping:
            filters[attribute_mapping[key]] = value

    # Find and filter ports
    ports = get_serial_ports()
    filtered_ports = []

    for port in ports:
        udev_info = get_udev_info(port)
        match = True

        for key, value in filters.items():
            if not re.search(f"{key}={re.escape(value)}", udev_info):
                match = False
                break

        if match:
            filtered_ports.append(port)

    return filtered_ports

def get_serial_port_info(port):
    # Mapping of udevadm keys to human-readable names
    attribute_mapping = {
        "ID_VENDOR_FROM_DATABASE": "vendor",
        "ID_MODEL_FROM_DATABASE": "model",
        "ID_USB_VENDOR": "usb_vendor",
        "ID_USB_MODEL_ENC": "usb_model",
        "ID_USB_MODEL_ID": "usb_model_id",
        "ID_VENDOR_ID": "vendor_id",
        "ID_SERIAL_SHORT": "serial",
    }

    # Run the udevadm command and get the output
    udev_info = get_udev_info(port)
    port_info = {}

    for line in udev_info.splitlines():
        if line.startswith('E: '):
            key, value = line[3:].split('=', 1)
            if key in attribute_mapping:
                # Decode escape sequences like \x20 to a space.
                # NOTE: Since only \x20 is common, we currently only replace that one
                port_info[attribute_mapping[key]] = value.replace('\\x20', ' ')

    return port_info

def find_serial_port(**kwargs):
    """
    Find a single serial port matching the provided filters.
    """
    ports = find_serial_ports(**kwargs)
    if len(ports) > 1:
        raise ValueError("Multiple matching ports found for filters: " + str(kwargs))
    elif len(ports) == 0:
        raise ValueError("No matching ports found for filters: " + str(kwargs))
    else:
        return ports[0]

Example: Find a serial port

# Example usage: Find a serial port
matching_ports = find_serial_ports(vendor="OpenMoko, Inc.")
print(matching_ports) # Prints e.g. ['/dev/ttyACM0']

Example: Print information about a given port

This is typically used so you know what filters to add for find_serial_ports().

# Example usage: Print info about a serial port
serial_port_info = get_serial_port_info('/dev/ttyACM0')
print(serial_port_info)

This prints, for example:

{
    'serial': '01010A23535223934CF29A1EF5000007',
    'vendor_id': '1d50',
    'usb_model': 'Marlin USB Device',
    'usb_model_id': '6029',
    'usb_vendor':
    'marlinfw.org',
    'vendor': 'OpenMoko, Inc.',
    'model': 'Marlin 2.0 (Serial)'
}