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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 validate(self, ticket=None):
 """ Validates all receipts matching this queryset. Note that, due to how AFIP implements its numbering, this method is not thread-safe, or even multiprocess-safe. Because of this, it is possible that not all instances matching this queryset are validated properly. Obviously, only successfully validated receipts will be updated. Returns a list of errors as returned from AFIP's webservices. An exception is not raised because partial failures are possible. Receipts that succesfully validate will have a :class:`~.ReceiptValidation` object attatched to them with a validation date and CAE information. Already-validated receipts are ignored. Attempting to validate an empty queryset will simply return an empty list. """

        # Skip any already-validated ones:
        qs = self.filter(validation__isnull=True).check_groupable()
        if qs.count() == 0:
            return []
        qs.order_by('issued_date', 'id')._assign_numbers()

        return qs._validate(ticket)