WhyNotHugo · rejjen · Jan 7, 2026 · Mar 8, 2026 · Mar 8, 2026 · WhyNotHugo
diff --git a/barcode/isxn.py b/barcode/isxn.py
@@ -66,17 +66,15 @@ class InternationalStandardBookNumber10(InternationalStandardBookNumber13):
 
     name = "ISBN-10"
 
-    digits = 9
+    isbn_digits = 9
 
     def __init__(self, isbn, writer=None) -> None:
-        isbn = isbn.replace("-", "")
-        isbn = isbn[: self.digits]
+        isbn = isbn.replace("-", "")[:self.isbn_digits]
+        self.isbn10 = f"{isbn}{self._calculate_checksum(isbn)}"
         super().__init__("978" + isbn, writer)
-        self.isbn10 = isbn
-        self.isbn10 = f"{isbn}{self._calculate_checksum()}"
 
-    def _calculate_checksum(self):
-        tmp = sum(x * int(y) for x, y in enumerate(self.isbn10[:9], start=1)) % 11
+    def _calculate_checksum(self, isbn):
+        tmp = sum(x * int(y) for x, y in enumerate(isbn[:self.isbn_digits], start=1)) % 11
         if tmp == 10:
             return "X"
 
@@ -99,29 +97,25 @@ class InternationalStandardSerialNumber(EuropeanArticleNumber13):
 
     name = "ISSN"
 
-    digits = 7
+    issn_digits = 7
 
     def __init__(self, issn, writer=None) -> None:
-        issn = issn.replace("-", "")
-        issn = issn[: self.digits]
-        self.issn = issn
-        self.issn = f"{issn}{self._calculate_checksum()}"
-        super().__init__(self.make_ean(), writer)
+        issn = issn.replace("-", "")[: self.issn_digits]
+        self.issn = f"{issn}{self._calculate_checksum(issn)}"
+        super().__init__(f"977{issn}00", writer) #checksum is overwritten by on .build
+
 
-    def _calculate_checksum(self):
+    def _calculate_checksum(self, issn):
         tmp = (
             11
-            - sum(x * int(y) for x, y in enumerate(reversed(self.issn[:7]), start=2))
+            - sum(x * int(y) for x, y in enumerate(reversed(issn[:self.issn_digits]), start=2))
             % 11
         )
         if tmp == 10:
             return "X"
 
         return tmp
 
-    def make_ean(self):
-        return f"977{self.issn[:7]}00{self._calculate_checksum()}"
-
     def __str__(self) -> str:
         return self.issn
 

diff --git a/barcode/itf.py b/barcode/itf.py
@@ -70,7 +70,7 @@ def build(self) -> list[str]:
                 raw += "0" * self.narrow
         return [raw]
 
-    def render(self, writer_options, text=None):
+    def render(self, writer_options: dict | None = None, text: str | None = None):
         options = {
             "module_width": MIN_SIZE / self.narrow,
             "quiet_zone": MIN_QUIET_ZONE,

diff --git a/pyproject.toml b/pyproject.toml
@@ -41,6 +41,9 @@ repository = "https://github.com/WhyNotHugo/python-barcode"
 issues = "https://github.com/WhyNotHugo/python-barcode/issues"
 funding= "https://whynothugo.nl/sponsor/"
 
+[dependency-groups]
+test = ["pytest", "coverage", "pillow", "cairosvg", "pyzbar"]
+
 [tool.setuptools.package-data]
 barcode = ["barcode/fonts/*.ttf"]
 

diff --git a/tests/test_with_pyzbar.py b/tests/test_with_pyzbar.py
@@ -0,0 +1,111 @@
+import pytest
+
+pytest.importorskip("pyzbar")
+pytest.importorskip("PIL")
+
+import os
+import barcode
+from barcode.base import Barcode
+from barcode.writer import ImageWriter, SVGWriter
+from pyzbar.pyzbar import decode
+from PIL import Image
+from io import BytesIO
+
+
+try:
+    import cairosvg
+    import cairocffi
+    cairocffi.Context(cairocffi.ImageSurface(cairocffi.FORMAT_ARGB32, 1, 1))
+    HAS_CAIROSVG = True
+except (ImportError, OSError):
+    HAS_CAIROSVG = False
+
+
+def get_normalized_code(barcode_instance: Barcode, code: str) -> str:
+    if isinstance(barcode_instance, barcode.UPCA) and len(code) > 12:
+        return code[-12:] ## return last 12, because may be leftpadded with zero from pyzbar.
+    return code
+
+
+def perform_pyzbar_validation(barcode_instance: Barcode, img: Image, from_svg: bool = False) -> None:
+    try:
+        classname = type(barcode_instance).name
+        decoded = decode(img)
+        assert decoded, f"{classname} failed to decode"
+    except AssertionError as e:
+        filename = f"pyzbar_decode_fail_{classname}{"_from_svg" if from_svg else ""}.png"
+        directory = os.path.join(os.path.dirname(os.path.abspath(__file__)), "test_outputs")
+        os.makedirs(directory, exist_ok=True)
+        img.save(os.path.join(directory, filename))
+        raise
+
+    normalized_code = get_normalized_code(barcode_instance, decoded[0].data.decode("ascii"))
+    fullcode_classes = (
+        barcode.Gs1_128,
+        barcode.ISBN10,
+        barcode.ISSN,
+    )
+    expected_code = str(barcode_instance if not isinstance(barcode_instance, fullcode_classes) else barcode_instance.get_fullcode())
+    assert normalized_code == expected_code, f"{classname}: invalid"
+    return True
+
+
+def get_valid_barcode_tuples() -> tuple[tuple[Barcode, str]]:
+    VALID_EAN8_CODE = "73513544"
+    VALID_EAN13CODE = "1000009029223"
+    VALID_BARCODES = (
+        (barcode.EAN8, VALID_EAN8_CODE),
+        (barcode.EAN8_GUARD, VALID_EAN8_CODE),
+        (barcode.EAN13, VALID_EAN13CODE),
+        (barcode.EAN13_GUARD, VALID_EAN13CODE),
+        (barcode.UPCA, "036000291452"),
+        (barcode.Code128, "A99BCDEF1234678"),
+        (barcode.Code39, "QWERTY"),
+        (barcode.JAN, "4901234567894"),
+        (barcode.ISSN, "1234567"), ## uses get_fullcode to validate, since __str__ returns issn value
+        (barcode.ISBN10, "306406152"), ## uses get_fullcode to validate, since __str__ returns isbn10 value
+        (barcode.ISBN13, "9783064061521"),
+        (barcode.Gs1_128, "YYYyyyy"), ## use get_fullcode to validate, since code prefixes with "\xf1" character on init
+        (barcode.ITF, "10000090292221"),
+        (barcode.PZN, "1234567"),
+        #(barcode.CODABAR, ""), ## pyzbar does not support decoding this
+        #(barcode.EAN14, "10000090292221"), ## pyzbar does not support decoding this, but I wonder if ITF is not essentially this, can't scan image with phone either. is useful for testing 
+    )
+    return VALID_BARCODES
+
+
+def test_imagewriter() -> None:
+    for barcode_class, valid_code in get_valid_barcode_tuples():
+        ## maybe consider using barcode.get_barcode() and using strings instead of classes.
+        barcode_instance = barcode_class(valid_code, writer=ImageWriter())
+        img = barcode_instance.render()
+
+        assert img, f"{type(barcode_instance).name} Failed to render"
+        perform_pyzbar_validation(barcode_instance, img)
+
+
+def test_ean14_png_decode_failure() -> None:
+    '''We expect this to fail for now, but if that stops this test can probably be removed. and added to get_valid_barcode_tuples'''
+    barcode_instance = barcode.get_barcode("EAN14", "10000090292221", writer=ImageWriter())
+    img = barcode_instance.render()
+    assert img, f"{type(barcode_instance).name} Failed to render"
+    try:
+        validation_success = perform_pyzbar_validation(barcode_instance, img)
+    except AssertionError:
+        validation_success = False
+    assert validation_success == False, "We expected failure, but this succeeded."
+
+
+@pytest.mark.skipif(not HAS_CAIROSVG, reason="cairosvg is not installed or can't load library")
+def test_svgwriter() -> None:
+    for barcode_class, valid_code in get_valid_barcode_tuples():
+        barcode_instance = barcode_class(valid_code, writer=SVGWriter())
+        svg_data = barcode_instance.render()
+        buf = BytesIO()
+        cairosvg.svg2png(bytestring=svg_data, write_to=buf, scale=2) ## scale it so antialiasing does not happen
+        buf.seek(0)
+        img = Image.open(buf)
+
+        assert img, f"{barcode_class} Failed to render"
+        perform_pyzbar_validation(barcode_instance, img, from_svg=True)
+