It's also for logging: log.debug(f"The value of counter was {counter}, the nonce was {nonce}") builds a new string every time the interpreter hits this li

It's also for logging: log.debug(f"The value of counter was {counter}, the nonce was {nonce}") builds a new string every time the interpreter hits this line. Whereas log.debug(t"The value of counter was {counter}, the nonce was {nonce}") passes a Template to the debug() function that bails out if debug mode is not on and doesn't build a string.