25.(str).replace()
替换
replace（oldstr，newstr，count)
用newstr替换oldstr，默认是全部替换，如果制定了count，那么直替换前count个
str44 = "AAAA is a good good good boy"
str45 = str44.replace("good","nice",1)
print(str45)
#(输出)sunck is a nice good good man #即将第一个good替换为nice