不知道咋写按照我的思路代码很长肯定不对,网上搜了好多也找不到我快哭了

string = input("请输入一个字符串: ")
string = string.lower()
letter_count = {}
for letter in string:
if letter.isalpha():
if letter in letter_count:
letter_count[letter] += 1
else:
letter_count[letter] = 1
for letter, count in letter_count.items():
print(f"{letter}: {count}次")