Appending List Elements to Another List (Python)

Question

I've made some code that has a list of new users and current users and checks to see if the username is available. If unavailable, it outputs a message saying so, otherwise outputs a message saying it's available. After this, I'm trying to append the elements of the new_users list to the current_users, on the condition that it doesn't already exist there. I would then like to print the current_users list to indicate the changes have occurred.

Here is my code so far - it only prints the current_users list without the changes still which is where my problem is.

current_users = ['alice', 'bob', 'mary', 'OSCAR', 'Simon']
new_users = ['jack', 'daniel', 'sue', 'mary', 'chris']

current_users_lower = [user.lower() for user in current_users]

for new_user in new_users:
    if new_user in current_users:
        print(f"{new_user} unavailable\n")
    else:
        print(f'{new_user} available')

if new_user not in current_users_lower:
    current_users_lower.append(new_user)
print(current_users_lower)

Thank you for any help in advance. I know question formatting is really important here so i've tried my best to ask it as clearly as possible.

Thanks!

Thank you to the user who edited my code - I thought copying the code directly from my IDE it would carry the format into the post. Didn't realise it needed more work. Cheers! — slowlearner02
– slowlearner02, Commented Jul 9, 2020 at 2:23

Celius Stingher · Accepted Answer · 2020-07-09 02:24:39Z

1

IIUC, my advice would be to add the append as part of the for loop, while also using current_users_lower instead of current_users. All in all it would end up like this:

current_users = ['alice', 'bob', 'mary', 'OSCAR', 'Simon']
new_users = ['jack', 'daniel', 'sue', 'mary', 'chris']

current_users_lower = [user.lower() for user in current_users]

for new_user in new_users:
    if new_user in current_users_lower:
        print(f"{new_user} unavailable\n")
    else:
        print(f'{new_user} available')
        print("Appending new user to list")
        current_users_lower.append(new_user)

print(current_users_lower)

answered Jul 9, 2020 at 2:24

Celius Stingher

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3 Comments

deadshot Over a year ago

you should also change new_user to lower

slowlearner02 Over a year ago

Thank you for the quick response and also assisting with my question formatting. Thanks a heap!!!

Celius Stingher Over a year ago

Cheers @slowlearner02 do come back if you have any other question, we're happy to help!

Cresht · Accepted Answer · 2020-07-09 02:23:31Z

1

You were simply missing an indent.

current_users = ['alice', 'bob', 'mary', 'OSCAR', 'Simon']
new_users = ['jack', 'daniel', 'sue', 'mary', 'chris']

current_users_lower = [user.lower() for user in current_users]

for new_user in new_users:
    if new_user in current_users:
        print(f"{new_user} unavailable")
    else:
        print(f'{new_user} available')
    if new_user not in current_users_lower:
        current_users_lower.append(new_user)
print(current_users_lower)

answered Jul 9, 2020 at 2:23

Cresht

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2 Comments

Cresht Over a year ago

The if statement was not indented

slowlearner02 Over a year ago

Can't believe it was as simple as an indentation error. Thank you!

Ryan Michael Albers · Accepted Answer · 2020-07-09 02:33:52Z

0

Your problem seems to be that you are only appending the last item of you new_users list to current_users_lower. Try adding the if statement that appends the list to your for loop.

current_users = ['alice', 'bob', 'mary', 'OSCAR', 'Simon']
new_users = ['jack', 'daniel', 'sue', 'mary', 'chris']

current_users_lower = [user.lower() for user in current_users]

for new_user in new_users:
    if new_user in current_users:
        print(f"{new_user} unavailable\n")
    else:
        print(f'{new_user} available')

    if new_user not in current_users_lower:
        current_users_lower.append(new_user)

print(current_users_lower)

answered Jul 9, 2020 at 2:33

Ryan Michael Albers

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1 Comment

slowlearner02 Over a year ago

Thank you! Such a positive and quick response from everyone here. Not sure why I felt so intimidated to post this now haha

TheTriad · Accepted Answer · 2020-07-09 03:24:33Z

0

It's because the statement was not in the for statement.

 current_users = ['alice', 'bob', 'mary', 'OSCAR', 'Simon']
new_users = ['jack', 'daniel', 'sue', 'mary', 'chris']

current_users_lower = [user.lower() for user in current_users]

for new_user in new_users:
    if new_user in current_users:
        print(f"{new_user} unavailable\n")
    else:
        print(f'{new_user} available')
        current_users_lower.append(new_user)
print(current_users_lower)

answered Jul 9, 2020 at 3:24

TheTriad

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Comments

정도유 · Accepted Answer · 2020-07-09 03:44:34Z

0

use set operation. it makes code simple.

current_users = ['alice', 'bob', 'mary', 'OSCAR', 'Simon']
new_users = ['jack', 'daniel', 'sue', 'mary', 'chris']

current_users_lower = set([user.lower() for user in current_users])
new_users = set([user.lower() for user in new_users])

print(f'{new_users.intersection(current_users_lower)} are unavailable')
really_new = new_users.difference(current_users_lower)
print(f'{really_new} are available')

print(current_users_lower.union(new_users))

answered Jul 9, 2020 at 3:44

정도유

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