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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):
 """ Raise ValidationError if the contact exists. """

        contacts = self.api.lists.contacts(id=self.list_id)['result']

        for contact in contacts:
            if contact['email'] == self.cleaned_data['email']:
                raise forms.ValidationError(
                    _(u'This email is already subscribed'))

        return self.cleaned_data['email']