[majewsky]

I'm immediately skeptical after seeing this example because I'm not sure if the first line parses as:

  if (x := f()) is not None:

or as:

  if x := (f() is not None):

[sametmax]

That's why parenthesis are mandatory.

[icebraining]

:= overrules everything except a comma, so it's the latter. Still, I agree it's potentially confusing.