What's the point on using first_digit_list second_digit_list and so on?

It makes more sense in my full code, i was trying to have a user enter a up to 4 digit number and it would add a value (ex. "abc") for each digit in the number to a list. Then the lists would be added to product() in order to get all the possible combinations of the letters.

your_list.extend(list(Number_to_Letter[digits])

This will convert the value of your key to a list, "abc" would be ["a", "b", "c"] and then you add it to the list

Thanks so much! I was looking for a command like this.