qrreader.get_qr_reader: raise instead of returning None

move MissingQrDetectionLib to core lib

electrum/gui/qt/qrreader/__init__.py

@@ -29,6 +29,7 @@ from PyQt5.QtWidgets import QMessageBox, QWidget
 from electrum.i18n import _
 from electrum.util import UserFacingException
 from electrum.logging import get_logger
+from electrum.qrreader import MissingQrDetectionLib
 
 from electrum.gui.qt.util import MessageBoxMixin, custom_message_box
 
@@ -102,7 +103,7 @@ def _scan_qrcode_using_qtmultimedia(
         callback: Callable[[bool, str, Optional[str]], None],
 ) -> None:
     try:
-        from .qtmultimedia import QrReaderCameraDialog, CameraError, MissingQrDetectionLib
+        from .qtmultimedia import QrReaderCameraDialog, CameraError
     except ImportError as e:
         icon = QMessageBox.Warning
         title = _("QR Reader Error")

electrum/gui/qt/qrreader/qtmultimedia/__init__.py

@@ -26,7 +26,7 @@
 from typing import Mapping
 
 from .camera_dialog import (QrReaderCameraDialog, CameraError, NoCamerasFound,
-                            NoCameraResolutionsFound, MissingQrDetectionLib)
+                            NoCameraResolutionsFound)
 from .validator import (QrReaderValidatorResult, AbstractQrReaderValidator,
                         QrReaderValidatorCounting, QrReaderValidatorColorizing,
                         QrReaderValidatorStrong, QrReaderValidatorCounted)

electrum/gui/qt/qrreader/qtmultimedia/camera_dialog.py

@@ -36,7 +36,7 @@ from PyQt5.QtCore import QSize, QRect, Qt, pyqtSignal, PYQT_VERSION
 
 from electrum.simple_config import SimpleConfig
 from electrum.i18n import _
-from electrum.qrreader import get_qr_reader, QrCodeResult
+from electrum.qrreader import get_qr_reader, QrCodeResult, MissingQrDetectionLib
 from electrum.logging import Logger
 
 from electrum.gui.qt.util import MessageBoxMixin, FixedAspectRatioLayout, ImageGraphicsEffect
@@ -58,10 +58,6 @@ class NoCamerasFound(CameraError):
 class NoCameraResolutionsFound(CameraError):
     ''' Raised internally if no usable camera resolutions were found. '''
 
-class MissingQrDetectionLib(RuntimeError):
-    ''' Raised if we can't find zbar or whatever other platform lib
-    we require to detect QR in image frames. '''
-
 class QrReaderCameraDialog(Logger, MessageBoxMixin, QDialog):
     """
     Dialog for reading QR codes from a camera
@@ -97,8 +93,6 @@ class QrReaderCameraDialog(Logger, MessageBoxMixin, QDialog):
 
         # Try to get the QR reader for this system
         self.qrreader = get_qr_reader()
-        if not self.qrreader:
-            raise MissingQrDetectionLib(_("The platform QR detection library is not available."))
 
         # Set up the window, add the maximize button
         flags = self.windowFlags()

electrum/qrreader/__init__.py

@@ -35,15 +35,17 @@ from .abstract_base import AbstractQrCodeReader, QrCodeResult
 _logger = get_logger(__name__)
 
 
-class MissingLib(RuntimeError):
+class MissingQrDetectionLib(RuntimeError):
-    ''' Raised by underlying implementation if missing libs '''
+    ''' Raised if we can't find zbar or whatever other platform lib
-    pass
+    we require to detect QR in image frames. '''
 
 
-def get_qr_reader() -> Optional[AbstractQrCodeReader]:
+def get_qr_reader() -> AbstractQrCodeReader:
     """
-    Get the Qr code reader for the current platform
+    Get the Qr code reader for the current platform.
+    Might raise exception: MissingQrDetectionLib.
     """
+    excs = []
     try:
         from .zbar import ZbarQrCodeReader
         return ZbarQrCodeReader()
@@ -59,5 +61,13 @@ def get_qr_reader() -> Optional[AbstractQrCodeReader]:
         """
     except MissingLib as e:
         _logger.exception("")
+        excs.append(e)
+
+    raise MissingQrDetectionLib(f"The platform QR detection library is not available.\nerrors: {excs!r}")
+
 
-    return None
+# --- Internals below (not part of external API)
+
+class MissingLib(RuntimeError):
+    ''' Raised by underlying implementation if missing libs '''
+    pass