Compare a string variable with a string attribute of an object

Question

I have a list of objects that contain information of a user such as their username, userID and other attributes. I have another list that contains strings of usernames. Usernames are unique and will not be identical to another user's.

From these two lists, I would like to find which users are in both lists based on their username.

When comparing the list of strings to the Name attribute of a user object, if two usernames that appear identical are found, the equality check returns false.

For example, if one of the user objects has a Username attribute of "Gerald" and in my list of usernames "Gerald" is an item in that list, when comparing the two it always returns false.

# users is a list of user objects. A user object has a Username attribute that stores a string.
# names is a list of strings of usernames.

for user in users:
    for name in names:
        # The if statement below always returns false.
        if name == user.Name:
            # perform desired operations when a match is found here...
            break

I do not understand why two strings in this scenario cannot be compared.

Can attributes of an object not be compared to a variable of the same data type?

Answer 1

You can convert both to sets of strings, and then use & to take the intersection of them. Elements appearing in the intersection are the ones that would be duplicates.

This approach is reasonably fast and should be O(N) on average.

user_names = {u.Name for u in users}  # set of strings consisting the names
other_names = set(names)  # convert list to set
duplicates = user_names & other_names
for matched_string in duplicates:
    this_is_a_match_so_do_things()

Answer 2

I found a solution that works:

for user in users:
    for name in names:
        if name.find(user.Name) == 0:
            # perform desired operations when a match is found here...
            break

Using the str.find() function works but only when it is used on a name in the list of strings, not list of objects.

Doing it the following way always returned false:

for user in users:
    for name in names:
        if user.Name.find(name) == 0:
            # perform desired operations when a match is found here...
            break