>>> import email.policy as p
>>> p.default
Policy()
>>> p.HTTP
Policy(["linesep='\\r\\n'", 'max_line_length=None'])

I think you wanted Policy(linesep='\r\n', max_line_length=None); the problem comes from __repr__ where a format field is replaced by a list, which should have been something ', '.join(args) instead.

I can commit this minor thing if you want, I just wanted to check if I was right first.