How can I improve this code?

Question

Django

Greetings.
I started to understand ajax requests in Django, and decided to validate the login field during registration "on the fly". "Poke method" wrote the following code. And everything seems to be working correctly, but it seems to me that there are more correct ways to solve this problem (especially in the view).
When the username field is changed in the form, a GET request is sent via jquery to the server, where it is validated and the result is returned and displayed on the page.
urls.py

urlpatterns = [
    ....
    url(r'^validate/username/$', validate_username, name='validate_username'),
]

views.py

def validate_username(request):

    username = request.GET.get('username')
    sign_up_fm = SignUpForm(request.GET)
    data = {}

    try:  # Тут не уверен что правильно
        for validator in sign_up_fm.fields['username'].validators:
            validator(username)

    except ValidationError as e:
        data['info'] = e.message

    if data.get('info'):
        is_okey = False
    else:
        is_okey = True
        data['info'] = 'Логин свободный'  # если ошибок не было, то в data['info'] пусто

    data['is_okey'] = is_okey

    return JsonResponse(data)

forms.py

class SignUpForm(forms.ModelForm):

    username = forms.CharField(max_length=30, required=True)

    password = forms.CharField(
        widget=forms.PasswordInput(attrs={'class': 'form-control'}))

    confirm_password = forms.CharField(
        widget=forms.PasswordInput(attrs={'class': 'form-control'}))

    class Meta:
        model = User
        fields = ['username', 'password', 'confirm_password']

    def __init__(self, *args, **kwargs):
        super(SignUpForm, self).__init__(*args, **kwargs)
        self.fields['username'].validators.append(forbidden_usernames_validator)
        self.fields['username'].validators.append(invalid_username_validator)
        self.fields['username'].validators.append(unique_username_ignore_case_validator)
        self.fields['username'].validators.append(username_length_max_validator)
        self.fields['username'].validators.append(username_length_min_validator)

    def clean(self):
        super(SignUpForm, self).clean()
        password = self.cleaned_data.get('password')
        confirm_password = self.cleaned_data.get('confirm_password')
        if password and password != confirm_password:
            self._errors['password'] = self.error_class(
                ['Пароли не совпадают!'])
        return self.cleaned_data


def forbidden_usernames_validator(value):

    forbidden_usernames = ['admin', ]

    if value.lower() in forbidden_usernames:
        raise ValidationError(u'Это зарезервирование слово')


def invalid_username_validator(value):

    abc = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'r', 'q', 's',
           't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_']

    for i in range(len(value)):
        if value[i] not in abc:
            raise ValidationError(u'Недопустимые символы ( {} )'.format(value[i]))


def unique_username_ignore_case_validator(value):
    if User.objects.filter(username__iexact=value).exists():
        raise ValidationError('Логин занят')


def username_length_min_validator(value):
    if len(value) < 4:
        raise ValidationError('Логин слишком короткий')


def username_length_max_validator(value):
    if len(value) > 20:
        raise ValidationError('Логин слишком длинннный)

Further in the template, depending on the answer, everything will be drawn.
Thank you)

Answer 1

Here is what you can do

def invalid_username_validator(value):

    abc = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','r','q','s',
           't','u','v','w','x','y','z','0','1','2','3','4','5','6','7','8','9','-','_']

    for i in range(len(value)):
        if value[i] not in abc:
            raise ValidationError(u'Недопустимые символы ( {} )'.format(value[i]))

like this example:

import re

c = "Иван"

if re.search('^[A-Za-z0-9]*$',c, re.UNICODE):  
 # если нужны только маленькие латинские [a-z0-9]
    # do something
else:
   # do something