code: def _diffSchema(diskSchema, memorySchema):
      
      diskSchema = set(diskSchema)
      memorySchema = set(memorySchema)
      diskOnly = diskSchema - memorySchema
      memoryOnly = memorySchema - diskSchema
      diff = []
      if diskOnly:
          diff.append('Only on disk:')
          diff.extend(map(repr, diskOnly))
      if memoryOnly:
          diff.append('Only in memory:')
          diff.extend(map(repr, memoryOnly))
      return '\n'.join(diff)
docs: Format a schema mismatch for human consumption.
  
      @param diskSchema: The on-disk schema.
  
      @param memorySchema: The in-memory schema.
  
      @rtype: L{bytes}
      @return: A description of the schema differences.