code: def tell(self):
          
          assert self.writable
          pos = ctypes.c_size_t()
          check_call(_LIB.MXRecordIOWriterTell(self.handle, ctypes.byref(pos)))
          return pos.value
docs: Returns the current position of write head.
  
          Examples
          ---------
          >>> record = mx.recordio.MXIndexedRecordIO('tmp.idx', 'tmp.rec', 'w')
          >>> print(record.tell())
          0
          >>> for i in range(5):
          ...     record.write_idx(i, 'record_%d'%i)
          ...     print(record.tell())
          16
          32
          48
          64
          80