code: def connect(self):
          
          if not driver_ok:
              logger.error("Visa driver NOT ok")
              return False
          visa_backend = '@py'  # use PyVISA-py as backend
          if hasattr(settings, 'VISA_BACKEND'):
              visa_backend = settings.VISA_BACKEND
  
          try:
              self.rm = visa.ResourceManager(visa_backend)
          except:
              logger.error("Visa ResourceManager cannot load resources : %s" %self)
              return False
          try:
              resource_prefix = self._device.visadevice.resource_name.split('::')[0]
              extras = {}
              if hasattr(settings, 'VISA_DEVICE_SETTINGS'):
                  if resource_prefix in settings.VISA_DEVICE_SETTINGS:
                      extras = settings.VISA_DEVICE_SETTINGS[resource_prefix]
              logger.debug('VISA_DEVICE_SETTINGS for %s: %r'%(resource_prefix,extras))
              self.inst = self.rm.open_resource(self._device.visadevice.resource_name, **extras)
          except:
              logger.error("Visa ResourceManager cannot open resource : %s" %self._device.visadevice.resource_name)
              return False
          logger.debug('connected visa device')
          return True
docs: establish a connection to the Instrument