循环浏览列表，使用while vs if检查列表中正在循环的项目

Question

书籍中的示例问题

如果我想查看pastrami的列表，并确保finished中没有熏牛肉，这很好：

orders = ['tuna sub', 'chicken parmasean', 'pastrami', 'chicken teryiaki', 'pastrami']
finished = []
for order in orders:
while 'pastrami' in orders:
orders.remove('pastrami')
print("preparing " + order + " ...")
finished.append(order)
for sandwich in finished:
print(sandwich + " is ready")
└─$ python3 sandwiches.py
preparing tuna sub ...
preparing chicken parmasean ...
preparing chicken teryiaki ...
tuna sub is ready
chicken parmasean is ready
chicken teryiaki is ready

但是使用CCD_ 3来检查CCD_。

orders = ['tuna sub', 'chicken parmasean', 'pastrami', 'chicken teryiaki', 'pastrami']
finished = []
for order in orders:
if order == 'pastrami':
orders.remove('pastrami')
print("preparing " + order + " ...")
finished.append(order)
for sandwich in finished:
print(sandwich + " is ready")

─$ python3 sandwiches.py
preparing tuna sub ...
preparing chicken parmasean ...
preparing pastrami ...
preparing pastrami ...
tuna sub is ready
chicken parmasean is ready
pastrami is ready
pastrami is ready

我不明白为什么会发生这种事？

Answer 1

也许你想否定你的if？

finished = []
for order in orders:
if order != 'pastrami':
print("preparing " + order + " ...")
finished.append(order)