I am trying to create a message based drivers using the pyvisa-py backend.
I am obviously missing something, somewhere.
How can I define the backend resource manager that will be used in lantz?

I tried to create a class for my driver something looking like:
class LantzSignalGenerator(MessageBasedDriver):
"""Lantz Signal Generator.
"""

DEFAULTS = {'ASRL': {'read_termination': '\n', 'baud_rate': 9600}}
__resource_manager = visa.ResourceManager("@py")

.....

and I have the error:
Traceback (most recent call last):
File "mydriver.py", line 20, in
inst = LantzSignalGenerator('ASRL/dev/ttyACM0::INSTR')
File "/home/bizarri/bin/miniconda3/lib/python3.4/site-packages/lantz/messagebased.py", line 299, in init
self.resource_manager = get_resource_manager()
File "/home/bizarri/bin/miniconda3/lib/python3.4/site-packages/lantz/messagebased.py", line 40, in get_resource_manager
_resource_manager = visa.ResourceManager()
File "/home/bizarri/bin/miniconda3/lib/python3.4/site-packages/pyvisa/highlevel.py", line 1488, in __new
visa_library = open_visa_library(visa_library)
File "/home/bizarri/bin/miniconda3/lib/python3.4/site-packages/pyvisa/highlevel.py", line 1460, in open_visa_library
return cls(argument)
File "/home/bizarri/bin/miniconda3/lib/python3.4/site-packages/pyvisa/highlevel.py", line 96, in new
raise OSError('Could not open VISA library:\n' + '\n'.join(errs))
OSError: Could not open VISA library:

That I interpret as the creation trying to find the "standard" ni backend (not installed).

When I directly changing the backend in Lantz messagebased.py file:

_resource_manager = None

_resource_manager = visa.ResourceManager("@py")

Everything works fine...

In the init of Lantz messagebased.py, it seems that the first thing done to look for the resource_manager via get_resource_manager()
self.__resource_manager = get_resource_manager()
Does it make sense??? Define like this, _resource_manager will always be None?
global _resource_manager
if _resource_manager is None:
_resource_manager = visa.ResourceManager()
return _resource_manager

I am certainly missing something trivial but unfortunately it is beyond my limited understanding of python.

Thanks in advance for your time and help.