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)
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。
girls = ['gujin','yangmi','zhengshuang']
my_girls = []
a = len(girls)
a = int(a)
while a >= 0:
a=a-1
if a >= 0:
girl = girls.pop()
my_girls.append(girl)
else:
break
for my_girl in my_girls:
print(my_girl)
while判断不要等号。while a > 0:
我自己是这么理解的，a是我定义的变量 按照我原来的写法，a分别为3，2，1，0，while要执行4次
但是我的girls列表，只满足执行3次就是空列表，取无可取