Raise exceptions when trying to construct invalid cameras

tests/test_camera/test_camera.py

@@ -6,6 +6,7 @@
 
 import zoloto.cameras
 from tests.strategies import marker_types
+from zoloto.exceptions import CameraOpenError
 from zoloto.marker_type import MarkerType
 
 
@@ -57,3 +58,20 @@ def test_get_no_camera_ids(mocker: MockerFixture) -> None:
     VideoCapture.return_value.isOpened.return_value = False
     discovered_ids = list(zoloto.cameras.camera.find_camera_ids())
     assert len(discovered_ids) == 0
+
+
+def test_cannot_create_unopened_camera(mocker: MockerFixture) -> None:
+    VideoCapture = mocker.patch("zoloto.cameras.camera.VideoCapture")
+    VideoCapture.return_value.isOpened.return_value = False
+    with pytest.raises(CameraOpenError):
+        zoloto.cameras.Camera(0, marker_type=MarkerType.APRILTAG_36H11)
+
+
+def test_cannot_create_unopened_snapshotcamera(mocker: MockerFixture) -> None:
+    VideoCapture = mocker.patch("zoloto.cameras.camera.VideoCapture")
+    VideoCapture.return_value.isOpened.return_value = False
+    camera = zoloto.cameras.camera.SnapshotCamera(
+        0, marker_type=MarkerType.APRILTAG_36H11
+    )
+    with pytest.raises(CameraOpenError):
+        camera.capture_frame()

tests/test_camera/test_camera_module.py

@@ -20,9 +20,15 @@ def test_exposes_file_camera(camera_name: str) -> None:
 
 
 @given(marker_types())
-def test_camera_requires_marker_size(marker_type: MarkerType) -> None:
+def test_camera_requires_marker_size(
+    marker_camera: zoloto.cameras.marker.MarkerCamera,
+    temp_image_file: Path,
+    marker_type: MarkerType,
+) -> None:
+    marker_camera.save_frame(temp_image_file)
+
     camera = zoloto.cameras.file.ImageFileCamera(
-        Path("test.png"), marker_type=marker_type
+        temp_image_file, marker_type=marker_type
     )
     with pytest.raises(ValueError):
         camera.get_marker_size(0)
@@ -31,11 +37,11 @@ class TestCamera(zoloto.cameras.file.ImageFileCamera):
         def get_marker_size(self, marker_id: int) -> int:
             return 200
 
-    camera = TestCamera(Path("test.png"), marker_type=marker_type)
+    camera = TestCamera(temp_image_file, marker_type=marker_type)
     assert camera.get_marker_size(0) == 200
 
     camera = zoloto.cameras.file.ImageFileCamera(
-        Path("test.png"),
+        temp_image_file,
         marker_type=marker_type,
         marker_size=200,
     )

tests/test_camera/test_file_camera.py

@@ -0,0 +1,21 @@
+from pathlib import Path
+
+import pytest
+
+from zoloto.cameras.file import ImageFileCamera, VideoFileCamera
+from zoloto.exceptions import CameraOpenError
+from zoloto.marker_type import MarkerType
+
+
+def test_video_camera_unknown_file() -> None:
+    with pytest.raises(CameraOpenError):
+        VideoFileCamera(
+            Path.cwd() / "missing.mp4", marker_type=MarkerType.APRILTAG_36H11
+        )
+
+
+def test_image_camera_unknown_file() -> None:
+    with pytest.raises(CameraOpenError):
+        ImageFileCamera(
+            Path.cwd() / "missing.png", marker_type=MarkerType.APRILTAG_36H11
+        )

zoloto/cameras/camera.py

@@ -4,6 +4,7 @@
 from cv2 import CAP_PROP_BUFFERSIZE, VideoCapture
 from numpy import ndarray
 
+from zoloto.exceptions import CameraOpenError
 from zoloto.marker_type import MarkerType
 
 from .base import BaseCamera
@@ -41,6 +42,9 @@ def __init__(
         self.camera_id = camera_id
         self.video_capture = self.get_video_capture(self.camera_id)
 
+        if not self.video_capture.isOpened():
+            raise CameraOpenError(f"Failed to open camera {self.camera_id}")
+
     def __repr__(self) -> str:
         return f"<{self.__class__.__name__}: {self.camera_id}>"
 
@@ -90,7 +94,10 @@ def __repr__(self) -> str:
         return f"<{self.__class__.__name__}: {self.camera_id}>"
 
     def get_video_capture(self, camera_id: int) -> VideoCapture:
-        return VideoCapture(camera_id)
+        capture = VideoCapture(camera_id)
+        if not capture.isOpened():
+            raise CameraOpenError(f"Failed to open camera {self.camera_id}")
+        return capture
 
     def capture_frame(self) -> ndarray:
         self.video_capture = self.get_video_capture(self.camera_id)

zoloto/cameras/file.py

@@ -4,7 +4,7 @@
 from cv2 import VideoCapture, imread
 from numpy import ndarray
 
-from zoloto.exceptions import CameraReadError
+from zoloto.exceptions import CameraOpenError, CameraReadError
 from zoloto.marker_type import MarkerType
 
 from .base import BaseCamera
@@ -20,18 +20,22 @@ def __init__(
         marker_type: MarkerType,
         calibration_file: Optional[Path] = None,
     ) -> None:
-        self.image_path = image_path
         super().__init__(
             marker_size=marker_size,
             marker_type=marker_type,
             calibration_file=calibration_file,
         )
+        self.image_path = image_path
+        self._frame = imread(str(self.image_path))
+
+        if self._frame is None:
+            raise CameraOpenError(f"Failed to read file {self.image_path}")
 
     def __repr__(self) -> str:
         return f"<{self.__class__.__name__}: {self.image_path}>"
 
     def capture_frame(self) -> ndarray:
-        return imread(str(self.image_path))
+        return self._frame
 
 
 class VideoFileCamera(
@@ -53,6 +57,9 @@ def __init__(
         self.video_path = video_path
         self.video_capture = VideoCapture(str(self.video_path))
 
+        if not self.video_capture.isOpened():
+            raise CameraOpenError(f"Failed to read file {self.video_path}")
+
     def __repr__(self) -> str:
         return f"<{self.__class__.__name__}: {self.video_path}>"
 

zoloto/exceptions.py

@@ -15,3 +15,7 @@ class CameraReadError(ZolotoException):
     def __init__(self, frame: Optional[ndarray]):
         self.frame = frame
         super().__init__()
+
+
+class CameraOpenError(ZolotoException):
+    pass