libusb error: LIBUSB_ERROR_NOT_FOUND

4 posts / 0 new

Wed, 01/19/2022 - 02:48

SDJ

Hi,

This week I received a LabJack U3-LV and I'm using it for reading analog signals using Python (3.8) and a MacBook Pro (13-inch, 2017, Four Thunderbolt 3 Ports, Catalina). I found that after plugging in the U3, I sometimes get the error:
libusb error: LIBUSB_ERROR_NOT_FOUND

This is after running code:
import u3

d = u3.U3()

However, the error disappears after running the code above twice, without disconnecting the U3. Therefore, a simple workaround is following code:

import u3
import sys

try:
    d = u3.U3()
except:
    try:
        d = u3.U3()
    except:
sys.exit()

Note: the U3 is detected by my computer if it generates the error mentioned above. I checked this with Terminal command:
ioreg -p IOUSB

Greetings
SDJ

Wed, 01/19/2022 - 10:26

LabJack Support

This is a known issue that

This is a known issue that first cropped up with macOS 10.15. It appears to be a macOS USB issue and Apple has been unresponsive to our support requests. We recommend retrying the the open call (like you are currently doing) as a workaround. Sorry for the inconvenience.

Wed, 01/19/2022 - 22:42

SDJ

Thank you for the fast relpy

Thank you for the fast relpy and for providing great products! I'm very pleased to have found an interface that works on a Mac and on Linux.

Tue, 01/25/2022 - 01:11

SDJ

Small update. To avoid a "too

Small update. To avoid a "too broad exception clause" warning when using PyCharm for the code above, try this:

import u3 import LabJackPython import sys def interface_check(): try: # First call d = u3.U3() except LabJackPython.NullHandleException: try: # Second call d = u3.U3() except LabJackPython.NullHandleException: # Closing the program sys.exit() def main(): interface_check() if __name__ == "__main__": main()