code: def get_wrapper_class(backend_name):
      
      try:
          return _WRAPPERS[backend_name]
      except KeyError:
          if backend_name == 'ni':
              from .ctwrapper import NIVisaLibrary
              _WRAPPERS['ni'] = NIVisaLibrary
              return NIVisaLibrary
  
      try:
          pkg = __import__('pyvisa-' + backend_name)
          _WRAPPERS[backend_name] = cls = pkg.WRAPPER_CLASS
          return cls
      except ImportError:
          raise ValueError('Wrapper not found: No package named pyvisa-%s' % backend_name)
docs: Return the WRAPPER_CLASS for a given backend.
  
      :rtype: pyvisa.highlevel.VisaLibraryBase