code: def get_files_crc32(self):
          
          if self.files_crc32 == {}:
              for i in self.get_files():
                  buffer = self.zip.read(i)
                  self.files_crc32[i] = crc32(buffer)
  
          return self.files_crc32
docs: Calculates and returns a dictionary of filenames and CRC32
  
          :return: dict of filename: CRC32