Case-insensitive comparison of lists

Question

I want to make a code that to see if each new username has already been used in a website.

I have this code:

current_users = ['Rachel', 'Ross', 'Chandler', 'Joey', 'Monica']

new_users = ['Janice', 'Ben', 'Phoebe', 'JOEY']

for new_user in new_users:
    if new_user in current_users:
    print (f'The username {new_user} is alreay in use. You need to enter a new username')

else:
    print (f'The username {new_user} is avaliable')

And this outputs:

The username Janice is avaliable
The username Ben is avaliable
The username Phoebe is avaliable
The username JOEY is avaliable

For "JOEY" the message to be printed was supposed to be this: "The username JOEY is alreay in use. You need to enter a new username".

How can I lowercase (or uppercase) the lists to make this code case-insensitive?

The simplest solution would be to lowercase all the values in `current_users` then use `if new_user.lower() in current_users` — Nick, Jun 11 '22 at 23:53
@AsishM. Not really, because creating a list with all of the lowercased names isn't the best approach for this particular case. See my answer for more details. — BrokenBenchmark, Jun 11 '22 at 23:57

BrokenBenchmark · Accepted Answer · 2022-06-12T00:02:40.570

You should create a set that contains all of the lowercased names. Then, to check whether a name can be used, look up the lowercased version of the name in the set:

names_in_use = {name.lower() for name in current_users}

for new_user in new_users:
    if new_user.lower() in names_in_use:
        print (f'The username {new_user} is already in use. You need to enter a new username')
    else:
        print (f'The username {new_user} is avaliable')

This outputs:

The username Janice is avaliable
The username Ben is avaliable
The username Phoebe is avaliable
The username JOEY is already in use. You need to enter a new username

Case-insensitive comparison of lists

1 Answers1