[Python-Dev] transitioning from % to {} formatting

[INADA Naoki]

What about using string prefix 'f'?

  f"{foo} and {bar}" % something == "{foo} and {bar}.format(something)

  s = f"{foo}"
  t = "%(bar)s"
  s + t  # raises Exception

Transition plan:
n: Just add F prefix. And adding "format_string" in future.
n+1: deprecate __mod__() without 'F'.
n+2: libraries use .format() and deprecate __mod__() with 'F'
n+3: remove __mod__()

-- 
Naoki INADA  <songofacandy at gmail.com>