code: def write(self, buf):
          
          assert self.writable
          self._check_pid(allow_reset=False)
          check_call(_LIB.MXRecordIOWriterWriteRecord(self.handle,
                                                      ctypes.c_char_p(buf),
                                                      ctypes.c_size_t(len(buf))))
docs: Inserts a string buffer as a record.
  
          Examples
          ---------
          >>> record = mx.recordio.MXRecordIO('tmp.rec', 'w')
          >>> for i in range(5):
          ...    record.write('record_%d'%i)
          >>> record.close()
  
          Parameters
          ----------
          buf : string (python2), bytes (python3)
              Buffer to write.