code: def header_size(self):
          
          standard_header_size = MRC_HEADER_SIZE
  
          try:
              extra_header_size = int(self.header['nsymbt']['value'])
          except KeyError:
              extra_header_size = 0
  
          return standard_header_size + extra_header_size
docs: Total size of `file`'s header (including extended) in bytes.
  
          The size of the header is determined from `header`. If this is not
          possible (i.e., before the header has been read), 0 is returned.
  
          If the header contains an ``'nsymbt'`` entry (size of the extra
          header in bytes), its value is added to the regular header size.