python一个关于while循环的报错问题

Question

girls = ['gujin','yangmi','zhengshuang']
my_girls = []
a = len(girls)
a = int(a)
while a >= 0:
a=a-1
girl = girls.pop()
my_girls.append(girl)
continue
for my_girl in my_girls:
print(my_girl)

报错：
Traceback (most recent call last):

File "girls4.py", line 6, in
girl = girls.pop()
IndexError: pop from empty list

这段执行不报错：
girls = ['gujin','yangmi','zhengshuang']
my_girls = []
while girls:
girl = girls.pop()
my_girls.append(girl)
for my_girl in my_girls:
print(my_girl)

Answer 1

执行循环语句时，当a=1，判断a>=0满足，执行a=a-1，此时a=0，继续判断，a>=0仍然满足，执行a=a-1,此时a=-1，执行girl = girls.pop()必然出错，因为索引下标从 0 开始，所以直接把 while a >= 0 改成 while a > 0，这样当a=0时会直接跳出循环，就不会报错了。