GS1 always starts with Character Set B #110

noperator-zz commented 2021年06月24日 00:35:11 +02:00 (Migrated from github.com)

Some codes can be encoded entirely with code C, but Code128() initializes self._charset = "B" unconditionally.
Also, due to the (non-numeric) FNC 1 character at the start of a GS1 barcode, the library will always start with character set B anyway, even if self._charset was set to "C". WhyNotHugo/python-barcode@83a0b4e877/barcode/codex.py (L175)

The effect is that a switch to Code C is added after FNC 1, when it could have just started with character set C instead.

Expected (ignore the slash):
START C -> FNC 1 -> 12 -> 00 -> 13 -> 00 -> 85
image

Actual:
START B -> FNC 1 -> CODE C -> 12 -> 00 -> 13 -> 00 -> 85
gs128

import barcode
from barcode.writer import ImageWriter
sn = 1200130085
# START B -> FNC 1 -> CODE C -> barcode (code C)
code = barcode.get("gs1_128", str(sn), writer=ImageWriter())
code.save("gs128")

Some codes can be encoded entirely with code C, but Code128() initializes self._charset = "B" unconditionally. Also, due to the (non-numeric) FNC 1 character at the start of a GS1 barcode, the library will always start with character set B anyway, even if self._charset was set to "C". https://github.com/WhyNotHugo/python-barcode/blob/83a0b4e87755f8dcb22c9cf35c52f6f3ae7a6993/barcode/codex.py#L175 The effect is that a switch to Code C is added after FNC 1, when it could have just started with character set C instead. Expected (ignore the slash): START C -> FNC 1 -> 12 -> 00 -> 13 -> 00 -> 85  Actual: START B -> FNC 1 -> CODE C -> 12 -> 00 -> 13 -> 00 -> 85  ``` import barcode from barcode.writer import ImageWriter sn = 1200130085 # START B -> FNC 1 -> CODE C -> barcode (code C) code = barcode.get("gs1_128", str(sn), writer=ImageWriter()) code.save("gs128") ```

audoh-tickitto commented 2021年07月06日 12:21:43 +02:00 (Migrated from github.com)

Similar issue with Code128, it starts with charset B so it will never switch to charset A as A is a subset of B (for alphanumeric barcodes, at least).

I think there are some characters in charset A which are not included in charset B, so I think we will just need something a bit more sophisticated (both for GS1 and Code128) than just starting in one charset and changing if that does not support.

I sort of think we should just have these exposed via the constructor, with automatic resolution used only if not explicitly specified there.

Similar issue with Code128, it starts with charset B so it will never switch to charset A as A is a subset of B (for alphanumeric barcodes, at least). I think there are some characters in charset A which are not included in charset B, so I think we will just need something a bit more sophisticated (both for GS1 and Code128) than just starting in one charset and changing if that does not support. I sort of think we should just have these exposed via the constructor, with automatic resolution used only if not explicitly specified there.

WhyNotHugo commented 2021年07月16日 14:27:05 +02:00 (Migrated from github.com)

Yup, makes sense. The "next charset" should be evaluated at the rather than hardcoded.

Yup, makes sense. The "next charset" should be evaluated at the rather than hardcoded.