Reset USB device from python

usb_reset.py

"""
    Example code for resetting the USB port that a Teensy microcontroller is
    attached to. There are a lot of situations where a Teensy or Arduino can
    end up in a bad state and need resetting, this code is useful for 
"""

import os
import fcntl
import subprocess


# Equivalent of the _IO('U', 20) constant in the linux kernel.
USBDEVFS_RESET = ord('U') << (4*2) | 20


def get_teensy():
    """
        Gets the devfs path to a Teensy microcontroller by scraping the output
        of the lsusb command
        
        The lsusb command outputs a list of USB devices attached to a computer
        in the format:
            Bus 002 Device 009: ID 16c0:0483 Van Ooijen Technische Informatica Teensyduino Serial
        The devfs path to these devices is:
            /dev/bus/usb/<busnum>/<devnum>
        So for the above device, it would be:
            /dev/bus/usb/002/009
        This function generates that path.
    """
    proc = subprocess.Popen(['lsusb'], stdout=subprocess.PIPE)
    out = proc.communicate()[0]
    lines = out.split('\n')
    for line in lines:
        if 'Teensyduino' in line:
            parts = line.split()
            bus = parts[1]
            dev = parts[3][:3]
            return '/dev/bus/usb/%s/%s' % (bus, dev)


def send_reset(dev_path):
    """
        Sends the USBDEVFS_RESET IOCTL to a USB device.
        
        dev_path - The devfs path to the USB device (under /dev/bus/usb/)
                   See get_teensy for example of how to obtain this.
    """
    fd = os.open(dev_path, os.O_WRONLY)
    try:
        fcntl.ioctl(fd, USBDEVFS_RESET, 0)
    finally:
        os.close(fd)


def reset_teensy():
    """
        Finds a teensy and reset it.
    """
    send_reset(get_teensy())

@rishta That's a great hint. Thanks.

Note to others: You have to pip install pyusb. If you pip install usb you get the only the wheel and can't import it.

What if the device isnt getting detected while connected? Any way to reset all USB ports and rescan?