pyvisa no longer able to load Keysight VISA in Python 3.8 on Windows

Python 3.8 changes .dll load behavior. See https://github.com/Toblerity/Fiona/issues/851

This used to work:

import pyvisa
rm = pyvisa.ResourceManager('ktvisa32')

… but now it doesn’t. The problem is that Keysight VISA stores a bunch of its .dll’s in a separate directory (not c:\windows\system32, but C:\Program Files (x86)\Keysight\IO Libraries Suite\bin) that is on the PATH. With the change in behavior, the PATH is no longer searched and so the ktvisa32.dll .dll fails to load because its dependant .dll’s can’t be found.

As a workaround, users can use the following syntax:

32-bit Python:

import os
os.add_dll_directory('C:\\Program Files (x86)\\Keysight\\IO Libraries Suite\\bin')
import pyvisa
rm = pyvisa.ResourceManager('ktvisa32')

64-bit Python:

import os
os.add_dll_directory('C:\\Program Files\\Keysight\\IO Libraries Suite\\bin')
import pyvisa
rm = pyvisa.ResourceManager('ktvisa32')

Feel free to reach out to me if you need someone to test a fix, or something ([e-mail])

[MatthieuDartiailh]

As per the discussion in this issue, it was decided to simply document the behavior and add the possibility to provide the additional path in the configuration file. No changes (that would have been Keysight and Windows specific) have been made to PyVISA.

If you think the documentation and/or the error message need to be improved feel free to open a PR. Adding additional details to the error message that would be Windows specific sounds perfectly doable for example.

[MarekPetr]

Using pyvisa-1.11.3 (installed using pip) in Python 3.8.7 I still had to use this code os.add_dll_directory('C:\\Program Files\\Keysight\\IO Libraries Suite\\bin') to avoid getting the error VI_ERROR_LIBRARY_NFOUND (-1073807202): A code library required by VISA could not be located or loaded. I have even tried the pyvisa version 1.10.0.rc with no success.