class_docstr: Backend storage for our "array of bits" using an mmap'd file.
  Please note that this has only been tested on Linux so far.
class_docstr_tok: ["Backend","storage","for","our","``","array","of","bits","''","using","an","mmap","'d","file",".","Please","note","that","this","has","only","been","tested","on","Linux","so","far","."]
docstr: Return true iff bit number bitno is set
code: def is_set(self, bitno):
      """Return true iff bit number bitno is set"""
      byteno, bit_within_wordno = divmod(bitno, 8)
      mask = 1 << bit_within_wordno
      byte = self.mmap[byteno]
      return byte & mask
  
imports: import array
  import math
  import os
  import random
label_desc: Use image node_id 2 for calling the Mmap_backend obj's underlying member method code with example usage: obj.is_set(bitno) and returns: unknown