code: def read(self, n):
          
          while len(self.pool) < n:
              self.cur = self.files.next()
              self.pool = numpy.append(self.pool,
                      self.fetch(self.cur), axis=0)
  
          rt = self.pool[:n]
          if n == len(self.pool):
              self.pool = self.fetch(None)
          else:
              self.pool = self.pool[n:]
          return rt
docs: return at most n array items, move the cursor.