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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def clean_email(self):
 """ Ensure the email address is not already registered. """

        email = self.cleaned_data.get("email")
        qs = User.objects.exclude(id=self.instance.id).filter(email=email)
        if len(qs) == 0:
            return email
        raise forms.ValidationError(
                                ugettext("This email is already registered"))