关于PYTHON字符串处理，怎么实现统计字符串中出现了2次的英文字母（区分大小写）

Question

问题相关代码，请勿粘贴截图

s=input()
dic={}
for i in s:
if i >='a' and i<='z' or i>='A' and i<='Z' :
dic[i]=s.count(i)
def getKey(dic,2):
if 2 not in dic:
return '出现2次的字母：无'
result=set()
for key in dic:
result.add(key)
return '出现2次的字母：',result

运行结果及报错内容

Exited with error status 1
File "/data/0d5b1f086b293b442a33aa0f857a4235", line 6
def getKey(dic,2):
^
SyntaxError: invalid syntax

我想要达到的结果

Answer 1

s = input()
a = []
for i in s:
    if s.count(i) == 2 and i not in a:
        a.append(i)
a = ",".join([str(i) for i in a])
print("出现2次的字母：无" if len(a) == 0 else "出现2次的字母：{}".format(a))