Django. Extend PasswordResetForm to check for email in database.

forms.py

from django.contrib.auth.forms import PasswordResetForm


class MailCheckPasswordResetForm(PasswordResetForm):
    email = forms.EmailField(max_length=254)

    error_messages = {
        'unknown': _("That email address doesn't have an associated "
                     "user account. Are you sure you've registered?"),
        'unusable': _("The user account associated with this email "
                      "address cannot reset the password."),
        }

    def clean_email(self):
        """
        Validates that an active user exists with the given email address.
        """
        email = self.cleaned_data["email"]
        self.users_cache = get_user_model()._default_manager.filter(email__iexact=email)
        if not len(self.users_cache):
            raise forms.ValidationError(self.error_messages['unknown'])
        if not any(user.is_active for user in self.users_cache):
            # none of the filtered users are active
            raise forms.ValidationError(self.error_messages['unknown'])
        if any((user.password == user.set_unusable_password())
            for user in self.users_cache):
            raise forms.ValidationError(self.error_messages['unusable'])
        return email

urls.py

url(r'^password_reset/$', auth_views.password_reset,
        {'template_name': 'accounts/password_reset/password_reset.html',
         'email_template_name': 'accounts/password_reset/password_reset_email.html',
         'post_reset_redirect': 'account:password_reset_done',
         'password_reset_form': PasswordResetForm}, # <---
        name='password_reset'),