code: def new(cls, arg):
          
          content = None
  
          if arg.kind == 'file':
              if os.path.exists(arg.value):
                  with open(arg.value, 'r') as f:
                      content = f.read()
              else:
                  raise Exception('File does not exist: {}'.format(arg.value))
          elif arg.kind == 'cli':
              content = arg.value
  
          for source_cls in cls.sources:
              if source_cls.supports_source(arg):
                  return source_cls(content)
  
          msg = 'Unsupported Parameter Source "{}"'
          raise Execption(msg.format(arg.value))
docs: Creates a new Parameter object from the given ParameterArgument.