如何在列表中交替使用字母/单词的大小写？

Question

I need to convert the "letter_guessed" input to lower case, if it's uppercase and if an uppercase letter already exists inside the list as a lower case it will return false but I can't get it to work.

I have tried using isupper() , upper , islower() , lower() in many ways. I am pretty sure that I am doing something wrong with "if" but can't get it right.

def check_valid_input(letter_guessed, old_letters_guessed):
    while True:
        """ will work only if you enter one letter and do not contain special letters other then the abc 
        and if its all ready been entered it will show false """

        if len(letter_guessed) == 1  and letter_guessed not in old_letters_guessed :
            """if the letter is one letter  and not already inside old_letter_guessed only then  continue """

            old_letters_guessed.append(letter_guessed)
            print("True")
            letter_guessed = input(" : ")

        else:
            """ if its wrong input will print False Try again and if the input is correct it will go back to " if " """

            #old_letters_guessed.append(letter_guessed)
            print(False, 'Try again')
            old_letters_guessed.sort()
            print('->'.join(old_letters_guessed))
            letter_guessed = input(" : ")
        #if letter_guessed is letter_guessed.isupper()

new = input()
old = []
check_valid_input(new,old)

Answer 1

Everything sting has a method called swapcase which swaps between upper and lower case. So:

"TEST".swapcase()

Would become

"test"

I'd suggest using that instead of your if statements.

Answer 2

use a for loop to iterate over all elements in the list with the .swapcase() function common to all strings

list = ['some', 'words', 'in a list']
for word in list:
    print(word.swapcase())