gpib-32.dll fails to load with Keysight Instrument Control Bundle

[TomasTollemark]

I have found a bug in the gpib-ctypes loading of DLL’s. It will fail if gpib-32.dll contains dependencies to other DLL’s outside the system32 directory.

For example the “Keysight_Instrument_Control_Bundle” installs the following files:
C:\Windows\System32\gpib-32.dll
C:\Program Files\Keysight\IO Libraries Suite\bin\ioPersistedDataAccess.dll

But ctypes calls LoadLibraryEx with dwFlags=LOAD_LIBRARY_SEARCH_DEFAULT_DIRS causing it to fail to load the ioPersistedDataAccess.dll since it is not in the System32 folder.

One solution is to set winmode=0 in ctypes like this:
_lib = ctypes.WinDLL(libname, winmode = 0)

My code changes are:

diff --git "a/gpib_orig.py" "b/gpib.py"
index 64bb0e8..b822ebc 100644
--- "a/gpib_orig.py"
+++ "b/gpib.py"
@@ -32,15 +32,16 @@ def _load_lib(filename=None):
                     'c:\\windows\\system\\gpib-32.dll',
                     'c:\\gpib\\gpib-32.dll',
                     'gpib-32.so', 'libgpib.so.0']
-        loader = ctypes.windll.LoadLibrary
     else:
         # most likely Linux with linux-gpib
         libnames = [filename] if filename else ['libgpib.so.0', 'gpib-32.so']
-        loader = ctypes.cdll.LoadLibrary
     for libname in libnames:
         try:
-            _lib = loader(libname)
+            if platform.system() == "Windows":
+                _lib = ctypes.WinDLL(libname, winmode = 0)
+            else:
+                _lib = ctypes.cdll.LoadLibrary(libname)
             break
         except OSError:
             continue