looping through a list, checking an item in the list being looped on using while vs if

Question

example problem from a book

if i wanted to check through the list for pastrami and make sure no pastrami ended up in finished, this works fine:

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

but using if to check order does not work.

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

I don't understand why this happens?

You print the order anyways, it will check and remove but `order` will still be saved as 'pastrami' — Matiiss, Apr 21 '21 at 13:28
Does this answer your question? [How to remove items from a list while iterating?](https://stackoverflow.com/questions/1207406/how-to-remove-items-from-a-list-while-iterating) — buran, Apr 21 '21 at 13:31

score 0 · Answer 1 · answered Apr 21 '21 at 13:30

0

Perhaps you meant to negate your if?

finished = []

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

answered Apr 21 '21 at 13:30

quamrana

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looping through a list, checking an item in the list being looped on using while vs if

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