def verify_check_digit(self, rcn: Rcn) -> None:
if self.check_digit_slice is None:
return None
value = rcn.value[self.value_slice]
check_digit = int(rcn.value[self.check_digit_slice])
calculated_check_digit = checksums.price_check_digit(value)
if check_digit != calculated_check_digit:
raise ParseError(
f"Invalid check digit for variable measure value {value!r} "
f"in RCN {rcn.value!r}: "
f"Expected {calculated_check_digit!r}, got {check_digit!r}.")
def _parse_using_british_price_rules(self: Rcn) -> None:
# References:
# https://www.gs1uk.org/how-to-barcode-variable-measure-items
if self.payload[:2] not in ("20", ):
return
check_digit = int(self.payload[-5])
value = self.payload[-4:]
calculated_check_digit = checksums.price_check_digit(value)
if check_digit != calculated_check_digit:
raise ParseError(
f"Invalid price check digit for price data {value!r} "
f"in RCN {self.value!r}: "
f"Expected {calculated_check_digit!r}, got {check_digit!r}.")
pounds_sterling = Decimal(value)
self.price = pounds_sterling / 100
def without_variable_measure(self, rcn: Rcn) -> Gtin:
# Zero out the variable measure part of the payload, and recalculate both
# the GTIN check digit and the variable measure's check digit digit, if any.
rcn_13 = rcn.as_gtin_13()
zeroed_value = "0" * len(rcn_13[self.value_slice])
digits = list(self.pattern)
digits[self.prefix_slice] = list(rcn_13[self.prefix_slice])
digits[self.value_slice] = list(zeroed_value)
if self.check_digit_slice is not None:
digits[self.check_digit_slice] = [
str(checksums.price_check_digit(zeroed_value))
]
gtin_payload = "".join(digits)
gtin_check_digit = checksums.numeric_check_digit(gtin_payload)
gtin = f"{gtin_payload}{gtin_check_digit}"
return Gtin.parse(gtin, rcn_region=rcn.region)
def without_variable_measure(self: Rcn) -> Gtin:
"""Create a new RCN where the variable measure is zeroed out.
This provides us with a number which still includes the item
reference, but does not vary with weight/price, and can thus be used
to lookup the relevant trade item in a database or similar.
This has no effect on RCNs intended for use within a company, as
the semantics of those numbers vary from company to company.
Returns:
A new RCN instance with zeros in the variable measure places.
Raises:
EncodeError: If the rules for variable measures in the region are unknown.
"""
if self.usage == RcnUsage.COMPANY:
return self
if self.region in (
RcnRegion.BALTICS,
RcnRegion.NORWAY,
RcnRegion.SWEDEN,
):
measure = "0000"
payload = f"{self.value[:-5]}{measure}"
check_digit = checksums.numeric_check_digit(payload)
value = f"{payload}{check_digit}"
return Gtin.parse(value, rcn_region=self.region)
elif self.region in (RcnRegion.GREAT_BRITAIN, ):
measure = "0000"
price_check_digit = checksums.price_check_digit(measure)
payload = f"{self.value[:-6]}{price_check_digit}{measure}"
check_digit = checksums.numeric_check_digit(payload)
value = f"{payload}{check_digit}"
return Gtin.parse(value, rcn_region=self.region)
else:
raise EncodeError(
f"Cannot zero out the variable measure part of {self.value!r} as the "
f"RCN rules for the geographical region {self.region!r} are unknown."
)
def test_price_check_digit(value: str, expected: int) -> None:
assert price_check_digit(value) == expected
def test_price_check_digit_on_values_with_wrong_length(value: str) -> None:
with pytest.raises(ValueError) as exc_info:
price_check_digit(value)
assert str(
exc_info.value) == f"Expected input of length 4 or 5, got {value!r}."
def test_price_check_digit_with_nonnumeric_value(value: str) -> None:
with pytest.raises(ValueError) as exc_info:
price_check_digit(value)
assert str(exc_info.value) == f"Expected numeric value, got {value!r}."