Python code runs in interactive prompt but not as script

Question

I am trying to interface with an Ocean optics spectrometer using seabreeze (seabreeze) and pyseabreeze (pyseabreeze).

If I enter python from the command prompt (cmd) in windows and enter the following code line by line, it works. However, if I put it in a script (spec_test.py) and try running it from cmd.exe by using 'python spec_test.py', it will not work.

I have searched around a lot for similar problems but none seem to cover the issue I'm having. I am running Windows 7 64 bit, python 3.5.2 installed using anaconda. I also had to install pyusb and libusb to use pyseabreeze.

The code:

import seabreeze
seabreeze.use('pyseabreeze')
import seabreeze.spectrometers as sb

devs = sb.list_devices()
print(devs)
spec = sb.Spectrometer(devs[0])
print(spec.model)

and the error message I get:

[<SeaBreezeDevice USB2000PLUS:FLMS02379>]
Traceback (most recent call last):
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\seabreeze\pyseabreeze\interfaces\common.py", line 14, in decorated_func
    return func(*args, **kwargs)
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\seabreeze\pyseabreeze\interfaces\spectrometer.py", line 46, in open
    self.open_device(device.handle)
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\seabreeze\pyseabreeze\interfaces\communication.py", line 37, in open_device
    device.set_configuration()
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\usb\core.py", line 869, in set_configuration
    self._ctx.managed_set_configuration(self, configuration)
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\usb\core.py", line 102, in wrapper
    return f(self, *args, **kwargs)
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\usb\core.py", line 148, in managed_set_configuration
    self.backend.set_configuration(self.handle, cfg.bConfigurationValue)
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\usb\backend\libusb0.py", line 493, in set_configuration
    _check(_lib.usb_set_configuration(dev_handle, config_value))
  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\usb\backend\libusb0.py", line 431, in _check
    raise USBError(errmsg, ret)
usb.core.USBError: [Errno None] b'libusb0-dll:err [set_configuration] could not set config 1: win error: The parameter is incorrect.\r\n'
Traceback (most recent call last):

  File "<ipython-input-9-ead886eb3666>", line 1, in <module>
    runfile('C:/Users/Raman Lab/Python code/Spectrometers/spec_testing.py', wdir='C:/Users/Raman Lab/Python code/Spectrometers')

  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 866, in runfile
    execfile(filename, namespace)

  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\spyder\utils\site\sitecustomize.py", line 102, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "C:/Users/Raman Lab/Python code/Spectrometers/spec_testing.py", line 7, in <module>
    spec = sb.Spectrometer(devs[0])

  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\seabreeze\spectrometers.py", line 62, in __init__
    self._open_device(device)

  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\seabreeze\spectrometers.py", line 90, in _open_device
    lib.device_open(self._dev)

  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\seabreeze\pyseabreeze\wrapper.py", line 81, in device_open
    return device.interface.open(device)

  File "C:\Users\Raman Lab\AppData\Local\Continuum\Anaconda3\lib\site-packages\seabreeze\pyseabreeze\interfaces\common.py", line 23, in decorated_func
    raise SeaBreezeError(msg)

SeaBreezeError: An error occured during opening.

Thanks for any help!

Edit: For some reason I figured this out, thought it might help describe the issue. If I enter interactive python from cmd.exe and paste the code instead of typing it in manually, I get the same error. This makes me think (most likely I'm wrong) that it is somehow tied up with speed of imports. I tried adding a sleep for a few seconds in between lines 3 and 5, to simulate what happens when I am typing in the prompt, but that didn't help. I hope this was descriptive enough.

Answer 1

Your initial guess was not far off. I had exactly the same problem, however, on Windows 7 32bit with Python 2.7. The example code gchaks linked to was running fine. When I tried executing the script several times in quick succession, the error message changed and pointed at a empty devices list. I added a delay of 2 seconds after

devs = sb.list_devices()

and that solved the problem. Your code was running just fine on a Linux machine btw.

Another hint: If your code should run once, but then you run into another error message, make sure you close the device connection or dis- and reconnect the spectrometer.