How to compare if a string is in a list and have each item in that list be read in lower()?

Question

I want to see if a new username already exists in a list of users, but for the existing users to also be evaluated user the lower() function.

I have already tried this:

for nuser in new_users:
        if nuser.lower() not in users.lower():

But it does not like the users.lower():

I have also tried changing my nuser.lower() to nuser.title(), but this is not future proof as I not all users will be writing in title() format.

My whole code below:

users = ['John', 'Kyle', 'Lily', 'admin', 'Tom']
new_users = ['john', 'Mike', 'TOM', 'Daemon']

if new_users:
    for nuser in new_users:
        if nuser.lower() not in users.lower():
            print("Username: "+nuser+" is available.")
        else:
            print("Username: "+nuser+" is not available, you will have to choose another.")

For example I expect TOM and Tom to clash and print that the username is not available.

Many thanks!

Mr_and_Mrs_D · Answer 1 · 2019-01-26T12:46:20.443

1

users = ['John', 'Kyle', 'Lily', 'admin', 'Tom']
new_users = ['john', 'Mike', 'TOM', 'Daemon']

if new_users:
    users_lower = set(map(str.lower, users))
    for nuser in new_users:
        if nuser.lower() not in users_lower:
            print("Username: "+nuser+" is available.")
        else:
            print("Username: "+nuser+" is not available, you will have to choose another.")

users is a list it has no attribute lower - you must lower the list elements your self and use a set for lookups to be fast (element in some_list is much slower than element in some_set)

edited Jan 26 '19 at 12:46

answered Jan 26 '19 at 12:44

Mr_and_Mrs_D

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2

Why not @Austin? – Mr_and_Mrs_D Jan 26 '19 at 12:48
Initially you posted the answer without any explanation and then you edited the answer to add explanation. – Arpit Svt Jan 26 '19 at 12:49
What do you mean @ArpitSvt? – Mr_and_Mrs_D Jan 26 '19 at 12:49
1

`Initially you posted the answer without any explanation and then you edited the answer to add explanation` So you downvoted for that? – Mr_and_Mrs_D Jan 26 '19 at 12:52

score 0 · Answer 2 · answered Jan 26 '19 at 12:53

0

users = ['John', 'Kyle', 'Lily', 'admin', 'Tom'] New_users = ['john', 'Mike', 'TOM', 'Daemon']

Why not lower using list comprehension as follow :

users_lower= [x.lower() for x in users]

And compare New_users lowered to match in that new lowered users list ?

answered Jan 26 '19 at 12:53

Drastik MoustiK

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It's better to use a `set`, as `users_lower` will only be used to test if it contains some item or not. See @Mr_and_Mrs_D's answer. – Thierry Lathuille Jan 26 '19 at 12:55
Cause he doesn't care about order and duplicates I suppose ? – Drastik MoustiK Jan 26 '19 at 12:58
As stated in the other answer, it is much faster: `item in some_set` is about O(1), `item in some_list` is O(len(some_list)). And of course, we don't care about order in this case. You can have a look at https://stackoverflow.com/questions/12354515/what-is-the-difference-between-sets-and-lists-in-python – Thierry Lathuille Jan 26 '19 at 13:02
Thank you for the sharing ! – Drastik MoustiK Jan 26 '19 at 13:42

How to compare if a string is in a list and have each item in that list be read in lower()?

2 Answers2