Enforcing a min length in Django password

Question

I am currently using django.contrib.auth.views.password_password_reset_confirm to change a user's password. This is how my urls look:

from django.contrib.auth import views as auth_views

url(r'^password/reset/confirm/(?P<uidb36>[0-9A-Za-z]+)-(?P<token>.+)/$',
    redirect_if_loggedin(auth_views.password_reset_confirm),
    name='auth_password_reset_confirm'),

Currently, I am doing it directly into the django trunk -

# django.contrib.auth.views
def clean_new_password2(self):
    password1 = self.cleaned_data.get('new_password1')
    password2 = self.cleaned_data.get('new_password2')
    if password1 and password2:
        if len(password1) < 8:
            raise forms.ValidationError(_("Password must be at least 8 chars."))
        if password1 != password2:
            raise forms.ValidationError(_("The two password fields didn't match."))
    return password2

Surely there must be a better way.

Answer 1

The code that I eventually wrote after understanding Arthur's accepted answer:

This is the inherited form:

class SetPasswordWithMinLengthForm(SetPasswordForm):
    """
    Inherited form that lets a user change set his/her password without
    entering the old password while validating min password length
    """
    def clean_new_password1(self):
        password1 = self.cleaned_data.get('new_password1')
        if len(password1) < 4:
            raise ValidationError("Password must be at least 4 chars.")
        return password1

In the urls.py you can instruct the view to use the custom form by specifing set_password_form:

url(r'^forgot_password/reset/(?P<uidb36>[0-9A-Za-z]+)-(?P<token>.+)/$',
                                                     'django.contrib.auth.views.password_reset_confirm',
                                                     {'set_password_form':SetPasswordWithMinLengthForm}),