code: def _checksum(in_file, block_size=65536):
      
      cs = hashlib.sha256()
      with open(in_file, "rb") as f:
          for block in iter(lambda: f.read(block_size), b''):
              cs.update(block)
      return cs.hexdigest()
docs: sha256 checksum, thanks to: https://gist.github.com/rji/b38c7238128edf53a181