其实实现这个功能非常简单, 只需要使用一个while循环就好了, 如果满足条件就break跳出循环. 示例代码如下:
#input and judge gender
while True:
gender = input("Please input your gender (m for male, f for female):")
if(gender =='m' or gender == 'f'):
break
else:
print("Error! you must input a valid letter!Please try again!\n")
continue