code: def add_file(self, name, file, filename=None, content_type=None):
          
          if isinstance(file, FileStorage):
              value = file
          else:
              if isinstance(file, string_types):
                  if filename is None:
                      filename = file
                  file = open(file, 'rb')
              if filename and content_type is None:
                  content_type = mimetypes.guess_type(filename)[0] or \
                                 'application/octet-stream'
              value = FileStorage(file, filename, name, content_type)
  
          self.add(name, value)
docs: Adds a new file to the dict.  `file` can be a file name or
          a :class:`file`-like or a :class:`FileStorage` object.
  
          :param name: the name of the field.
          :param file: a filename or :class:`file`-like object
          :param filename: an optional filename
          :param content_type: an optional content type