Add exception when grabbing fails (#46)

* adding exception when grabbing fails

* Automatically reformatting code with black and isort

* updating __init__.py

* Automatically reformatting code with black and isort

---------

Co-authored-by: Auto-format Bot <[email protected]>

src/framegrab/__init__.py

@@ -1,4 +1,5 @@
 from .cli.clitools import preview_image
+from .exceptions import GrabError
 from .grabber import FrameGrabber
 from .motion import MotionDetector
 from .rtsp_discovery import AutodiscoverModes, ONVIFDeviceInfo, RTSPDiscovery
@@ -17,7 +18,7 @@
 __all__ = [
     "FrameGrabber",
     "MotionDetector",
-    "RTSPDiscovery",
+    "GrabError" "RTSPDiscovery",
     "ONVIFDeviceInfo",
     "AutodiscoverModes",
     "preview_image",

src/framegrab/exceptions.py

@@ -0,0 +1,6 @@
+class GrabError(Exception):
+    """Exception raised for errors in the frame grabbing process."""
+
+    def __init__(self, message="Failed to grab frame from camera."):
+        self.message = message
+        super().__init__(self.message)

src/framegrab/grabber.py

@@ -13,6 +13,7 @@
 import numpy as np
 import yaml
 
+from .exceptions import GrabError
 from .rtsp_discovery import AutodiscoverModes, RTSPDiscovery
 from .unavailable_module import UnavailableModule
 
@@ -356,6 +357,11 @@ def grab(self) -> np.ndarray:
         """
         frame = self._grab_implementation()
 
+        if frame is None:
+            name = self.config["name"]  # all grabbers should have a name, either user-provided or generated
+            error_msg = f"Failed to grab frame from {name}"
+            raise GrabError(error_msg)
+
         # apply post processing operations
         frame = self._crop(frame)
         frame = self._digital_zoom(frame)