code: def _get_signature(self, entry):
          
  
          if self._sha1_sigs:
              # return sha1 digest of the file content...
              if not os.path.exists(entry.filename):
                  return None
              try:
                  with open(entry.filename, "r") as f:
                      data = f.read()
                      return hashlib.sha1(data.encode("utf-8")).digest()
              except IOError as e:
                  print("Cannot determine sha1 digest:", e)
                  return None
          else:
              # return file modification date...
              try:
                  return os.path.getmtime(entry.filename)
              except OSError:
                  return None
docs: Return the signature of the file stored in entry.