[Python] Why there is f prepended to the values [duplicate]

In this repo, lines 11&49, a letter f is prepended to the values,ie,

f'{path}/*'


and

f'data_{idx}'


why?

i have searched online that there is explanation for this. a letter f should be included within single or double quotes. but it's strange that i could run this piece of code perfectly fine on my machine

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