How to prevent usernames from containing @/./+/-/_.?

Question

I\'m using django-allauth, and for some reason the username default allows:

\"letters, digits and @/./+/-/_.\"

How can I ensure usernames are strictly alphanumer

Answer 1

I haven't used django and certainly don't know about its authorisation mechanisms, but I know that in plain python, if you wanted to carry this out, you could simply sanitise input by doing:

newUserName = ''.join(ch for ch in oldUserName if ch.isalnum())

Essentially, I'm looping through each character and am appending them to the 'clean' username if the character is alphanumeric.

In your function, if the username doesn't comply with the alphanumeric restrictions, execute the statement above (place it under the if).

Answer 2

You could use a regex expression to ensure that a username contains only allowed characters. For alphanumeric characters the following should do the trick:

import re
def is_valid_username(username):
    pattern = re.compile('([a-zA-Z]+|\d+)')
    return ''.join(re.findall(pattern, username)) == username

Here's an example of the output:

username_list = ["WhatAGre4tUsern4me", "548ThatISAgoodUsername005",
                 "CheckOutMy_Username", "It'sAUsern@me"]
print([is_valid_username(u) for u in username_list])
>>> [True, True, False, False]

Answer 3

I think python's builtin function str.isalnum() could be usefull here.

class UsernameMaxAdapter(DefaultAccountAdapter):
    def clean_username(self, username):
        # assumes "username" is a type of "str" object
        if not username.isalnum():
            raise ValidationError("Use only alphanumeric characters")
        # your logic

UPDATE-1
set ACCOUNT_USERNAME_VALIDATORS in settings.py as mentioned in documentation

class CustomValidator(object):

    def __call__(self, username="", *args, **kwargs):
        username = username.isalnum()
        if not username:
            raise ValidationError("Use only alphanumeric characters")

in your settings.py,

custom_username_validators = [CustomValidator()]
ACCOUNT_USERNAME_VALIDATORS = 'path.to.settings.custom_username_validators'