--decode

Because I want a warning when libzbar is not available, but I don't want
that warning to be shown by default, unless the user explicitly asks for
--decode.

qr2text.py

@@ -12,6 +12,12 @@
 from typing import BinaryIO, Iterable, List, Optional, Tuple, Union
 
 
+try:
+    from pyzbar import pyzbar
+except ImportError:  # pragma: nocover
+    pyzbar = None
+
+
 __version__ = '1.0.1.dev0'
 
 
@@ -301,20 +307,17 @@ def from_svg(cls, fileobj: FileNameOrFileObject) -> 'QR':
         return qr
 
     def decode(self) -> Optional[bytes]:
-        try:
-            from pyzbar.pyzbar import ZBarSymbol, decode
-        except ImportError:  # pragma: nocover
-            # should I print a warning about libzbar not being available?
+        if pyzbar is None:
             return None
 
         # Note: experiments with pyqrcode and zbarimg show that I need
         # pyqrcode.create('text').svg('file.svg', background='#fff', scale=2)
         # to have recognizable qr codes.  no background or scale=1 make zbarimg
         # fail to find any codes.
         scale = 2
-        res = decode((self.canvas.to_bytes(xscale=scale, yscale=scale),
-                      self.size * scale, self.size * scale),
-                     symbols=[ZBarSymbol.QRCODE])
+        image_data = (self.canvas.to_bytes(xscale=scale, yscale=scale),
+                      self.size * scale, self.size * scale)
+        res = pyzbar.decode(image_data, symbols=[pyzbar.ZBarSymbol.QRCODE])
         assert 0 <= len(res) <= 1
         if not res:
             return None
@@ -341,13 +344,20 @@ def main() -> None:
                         help='remove empty border')
     parser.add_argument("--pad", type=int, default=0,
                         help='pad with empty border')
+    parser.add_argument("--decode", action="store_true",
+                        default=(pyzbar is not None),
+                        help=("decode the QR codes"
+                              " (default if libzbar is available)"))
     parser.add_argument("--no-decode", action="store_false",
-                        dest="decode", default=True,
+                        dest="decode",
                         help="don't decode the QR codes")
     parser.add_argument("filename", type=argparse.FileType('rb'), nargs='+',
                         help='SVG file with the QR code (use - for stdin)')
     args = parser.parse_args()
 
+    if args.decode and pyzbar is None:
+        print("libzbar is not available, --decode ignored", file=sys.stderr)
+
     rc = 0
     try:
         for filename in args.filename:

tests.py

@@ -4,6 +4,7 @@
 import pyqrcode
 import pytest
 
+import qr2text
 from qr2text import QR, Canvas, Error, Path, PathParser, main
 
 
@@ -317,6 +318,19 @@ def test_main(monkeypatch, tmp_path, capsys):
     ]) + '\n'
 
 
+def test_main_no_libzbar(monkeypatch, tmp_path, capsys):
+    filename = str(tmp_path / 'hello.svg')
+    pyqrcode.create('hello').svg(filename)
+    monkeypatch.setattr(sys, 'argv', ['qr2text', '--decode', filename])
+    monkeypatch.setattr(qr2text, 'pyzbar', None)
+    with pytest.raises(SystemExit) as exc:
+        main()
+    assert exc.value.code == 0
+    assert capsys.readouterr().err == '\n'.join([
+        'libzbar is not available, --decode ignored',
+    ]) + '\n'
+
+
 def test_main_error(monkeypatch, tmp_path, capsys):
     hello_svg = tmp_path / 'hello.svg'
     hello_svg.write_text('this is not an SVG file\n')