code: def header_size(self):
          
          if not self.header:
              return 0
  
          # Determine header size by finding the largest offset and the
          # value of the corresponding entry. The header size is the
          # offset plus the size of the entry.
          max_entry = max(self.header.values(),
                          key=lambda val: val['offset'])
          return max_entry['offset'] + max_entry['value'].nbytes
docs: Size of `file`'s header 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.