code: def seek(self, offset, whence=os.SEEK_SET):
          
          assert isinstance(offset, int)
          assert whence in (os.SEEK_SET, os.SEEK_CUR, os.SEEK_END)
  
          new_position = 0
          if whence == os.SEEK_SET:
              new_position = offset
          elif whence == os.SEEK_CUR:
              new_position = self.pos + offset
          elif whence == os.SEEK_END:
              new_position = self.max_size + offset
  
          if new_position < 0:
              return -1
  
          self.pos = new_position
  
          return self.pos
docs: Repositions the file C{offset} according to C{whence}.
          Returns the resulting offset or -1 in case of error.
          :rtype: int
          :return: the file offset.