Python 3.6 introduces F-strings as a new way of doing string formatting.

Instead of writing this:

def say(greeting='hello', target='world'):
    print('%s, %s!' % (greeting.title(), target))

... you can now write this:

def say(greeting='hello', target='world'):
    print(f'{greeting.title()}, {target}!')

This project provides automatic translation of old %-style formatting to the new string interpolation method using F-strings.

If you use Vim, then simply source the fstrings.vim file. Select a set of lines (with V) and press = to update the selection.

If you use another editor, you can invoke the fstrings.py script as follows:

python3.6 fstrings.py 40 50 < input.py > tmp.py

This parses all of input.py and outputs just lines 40-50 to tmp.py.