Case Sensitivity

[hbknjr]

Assuming your current_users list is all lowercase. You just need to convert your new_user name into lowercase before checking if it's in the current_users list.

You can do that with .lower() function.

current_users=['sandra', 'brigita', 'bri','deivis', 'raimis']
new_users=['bri', 'billy', 'minde', 'erika', 'edminrika', 'RAIMIS']
for new_user in new_users:
    if new_user.lower() in current_users:
        print(new_user+" "+"already exists."+" "+"You need to choose a different name.\n")
    else:
        print(new_user+" "+"is available.")