code: def read(self, file_des, num_bytes):
          
          file_handle = self.filesystem.get_open_file(file_des)
          file_handle.raw_io = True
          return file_handle.read(num_bytes)
docs: Read number of bytes from a file descriptor, returns bytes read.
  
          Args:
              file_des: An integer file descriptor for the file object requested.
              num_bytes: Number of bytes to read from file.
  
          Returns:
              Bytes read from file.
  
          Raises:
              OSError: bad file descriptor.
              TypeError: if file descriptor is not an integer.