python改变字符串的大小写

def flag_words_contain_e(words_list):
words=['zebra',"hEn",'doG']
s = 0
for i in words:
if 'e' in i or 'E' in i:
res1 = i[0].upper()
res2 = i[1:].lower()
words[s] = res1 + res2
else:
words[s] = i.lower()
s += 1
print(words)
代码好像是错的，但是我不会用这个函数，应该怎么改呢

def flag_words_contain_e(words):

    for i in range(len(words)):
        if 'e' in words[i] or 'E' in words[i]:
            words[i]=words[i].capitalize()
        else:
            words[i] = words[i].lower()
            
    print(words)
words_list=['zebra',"hEn",'doG']
flag_words_contain_e(words_list)

import  string;
def flag_words_contain_e(words_list):
    s = 0
    for i in words_list:
        if 'e' in i or 'E' in i:
            words_list[s] = i.capitalize()
        else:
            words_list[s] = i.lower()
        s += 1
    return words_list

words=['zebra',"hEn",'doG']
print(flag_words_contain_e(words))

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