Allow for specifiying "TcAdsDll.dll" location

[premnetsuwan-tpeng]

Hi! I'm using pyads on windows I'm interested in being able to specify the location of the ads dll.

Currently, pyads seems to check if the dll is in system directories, the directory of the python executable, and if "$TWINCAT3DIR" is set then "$TWINCAT3DIR/Common64".

pyads/src/pyads/pyads_ex.py

Lines 57 to 71 in 54a3418

	# load dynamic ADS library
	if platform_is_windows(): # pragma: no cover, skip Windows test
	dlldir_handle = None
	if sys.version_info >= (3, 8) and "TWINCAT3DIR" in os.environ:
	# Starting with version 3.8, CPython does not consider the PATH environment
	# variable any more when resolving DLL paths. The following works with the default
	# installation of the Beckhoff TwinCAT ADS DLL.
	dll_path = os.environ["TWINCAT3DIR"] + "\\.."
	if platform.architecture()[0] == "64bit":
	dll_path += "\\Common64"
	else:
	dll_path += "\\Common32"
	dlldir_handle = os.add_dll_directory(dll_path)
	try:
	_adsDLL = ctypes.WinDLL("TcAdsDll.dll") # type: ignore

For distribution of my app, it is somewhat cumbersome to install the dll in one of these directories and it would be convenient if I could set it to something local.

[chrisbeardy]

sounds sensible, how do you create routes to your PLC? These places are only checked if you are on Windows where you normally need to have TwinCat installed to create the route which means the dll is available.