Feedback on my first Python module

[snippsat]

Some use of string formatting but could be more,not so nice + ' ' +.
f-string makes it a lot nicer,that will of course make it 3.6 only.
if that's no problem then use f-string.

# You
run_command('mv ' + path + ' ' + path + '.old')

# f-string
run_command(f'mv {path} {path}.old')

# format() <-- 3.5
run_command('mv {0} {1}.old'.format(path, path))

with open() can be written in one statement,some like this as some not.

with open(path) as infile,open(f'{path}.new', 'w') as outfile:
    ...