SyntaxWarning twice during installaton

I just installed pelican and got syntax warning twice during installation

1) The release of Ubuntu
$ lsb_release -rd
Description: Ubuntu 20.04.2 LTS
Release: 20.04

2) The version of the package
$ apt-cache policy pelican
pelican:
  Installed: 4.0.1+dfsg-1
  Candidate: 4.0.1+dfsg-1
  Version table:
 *** 4.0.1+dfsg-1 500

3) What you expected to happen
smooth installation without warnings

4) What happened instead
snapshot from apt install
===
Setting up pelican (4.0.1+dfsg-1) ...
/usr/lib/python3/dist-packages/pelican/tools/pelican_themes.py:84: SyntaxWarning: "is" with a literal. Did you mean "=="?
  if args.action is 'list':
/usr/lib/python3/dist-packages/pelican/tools/pelican_themes.py:86: SyntaxWarning: "is" with a literal. Did you mean "=="?
  elif args.action is 'path':
===