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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_account(self):
 """Ensure this is an income account"""

        account = self.cleaned_data['account']
        if not account:
            return

        if account.type != Account.TYPES.income:
            raise ValidationError('Account must be an income account')

        try:
            account.housemate
        except Housemate.DoesNotExist:
            pass
        else:
            raise ValidationError('Account already has a housemate')

        return account