code: def get_open_file(self, file_des):
          
          if not is_int_type(file_des):
              raise TypeError('an integer is required')
          if (file_des >= len(self.open_files) or
                  self.open_files[file_des] is None):
              self.raise_os_error(errno.EBADF, str(file_des))
          return self.open_files[file_des][0]
docs: Return an open file.
  
          Args:
              file_des: File descriptor of the open file.
  
          Raises:
              OSError: an invalid file descriptor.
              TypeError: filedes is not an integer.
  
          Returns:
              Open file object.