code: def _get_fields_convert_map(self, fields, download=False):
          
          _f = fields
          t = {}
  
          # add support for download field
          def _get(name):
              _name = '_convert_download_{}'.format(name)
              if download and hasattr(self, _name):
                  return getattr(self, _name)
              return getattr(self, '_convert_{}'.format(name))
  
          if isinstance(_f, list):
              for k in _f:
                  if isinstance(k, str):
                      t[k] = _get(k)
                  elif isinstance(k, (tuple, list)):
                      name = k[0]
                      func = k[1]
                      if isinstance(func, str):
                          t[name] = _get(func)
                      elif callable(func):
                          t[name] = func
                      else:
                          raise ValueError("Fields convert function should be str or callable, but %r found" % type(func))
                  else:
                      raise ValueError("Fields convert element should be str or tuple or list, but %r found" % type(k))
          elif isinstance(_f, dict):
              for k, v in _f.items():
                  if isinstance(v, str):
                      t[k] = _get(v)
                  elif callable(v):
                      t[k] = v
                  else:
                      raise ValueError("Fields convert function should be str or callable, but %r found" % type(func))
          return t
docs: process fields_convert_map, ListView doesn't support list type but dict
  
          fields_convert_map should be define as list or dict
          for list, it can be:
              [name, name, ...]
              [(name, func), (name, func), ...] if func is str, it'll be the property name of class
          for dict, it can be:
              {'name':func, ...}
          :param model: model object
          :param parameters:
          :param prefix: it'll used to combine prefix+_convert_xxx to get convert function
              from class
          :return: