docs: def read_header_at( cls, f):
          """
          Given an open file-like object, read a block header
          from it and return it as a dict containing:
          * version (int)
          * prev_block_hash (hex str)
          * merkle_root (hex str)
          * timestamp (int)
          * bits (int)
          * nonce (ini)
          * hash (hex str)
          """
          header_parser = BlockHeaderSerializer()
          hdr = header_parser.deserialize( f )
          h = {}
          h['version'] = hdr.version
          h['prev_block_hash'] = "%064x" % hdr.prev_block
          h['merkle_root'] = "%064x" % hdr.merkle_root
          h['timestamp'] = hdr.timestamp
          h['bits'] = hdr.bits
          h['nonce'] = hdr.nonce
          h['hash'] = hdr.calculate_hash()
          return h