fmt-str.py

from string import Template

def main():
  x = 'world'

  # I.
  print(f'hello {x}!')

  # II.
  print('hello {}!'.format(x))

  # III.
  print('hello %s!' % x)

  # IV.
  t = Template('hello $x!')
  print(t.substitute(x=x))

  # lol
  (lambda s: print('hello {}!'.format(f'{"%s" % Template("$s").substitute(s=s)}')))(x)

if __name__ == '__main__':
  main()