Add webcam and plot python example

examples/python-dataflow/dataflow.yml

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+communication:
+  zenoh:
+    prefix: /example-python-dataflow
+
+nodes:
+  - id: node-1
+    operators:
+    - id: python_webcam
+      python: webcam_operator.py
+      inputs:
+        timer: dora/timer/millis/100
+      outputs:
+        - image
+
+  - id: node-2
+    operators:
+    - id: python_plot
+      python: plot_cv2.py
+      inputs:
+        image: node-1/python_webcam/image

examples/python-dataflow/plot_cv2.py

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+from enum import Enum
+from typing import Callable
+
+import cv2
+import numpy as np
+
+
+class DoraStatus(Enum):
+    CONTINUE = 0
+    STOP = 1
+
+
+class Operator:
+    """
+    Example operator incrementing a counter every times its been called.
+
+    The current value of the counter is sent back to dora on `counter`.
+    """
+
+    def __init__(self):
+        self.counter = 0
+
+    def on_input(
+        self,
+        input_id: str,
+        value: bytes,
+        send_output: Callable[[str, bytes], None],
+    ) -> DoraStatus:
+        """Handle input by incrementing count by one.
+
+        Args:
+            input_id (str): Id of the input declared in the yaml configuration
+            value (bytes): Bytes message of the input
+            send_output (Callable[[str, bytes]]): Function enabling sending output back to dora.
+        """
+        self.counter += 1
+        if input_id == "image":
+            frame = np.frombuffer(value, dtype="uint8")
+            frame = np.reshape(frame, (480, 640, 3))
+            cv2.imshow("frame", frame)
+            if cv2.waitKey(1) & 0xFF == ord("q"):
+                return DoraStatus.STOP
+        if self.counter > 20:
+            return DoraStatus.STOP
+        else:
+            return DoraStatus.CONTINUE
+
+    def drop_operator(self):
+        cv2.destroyAllWindows()

examples/python-dataflow/requirements.txt

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+pip install opencv-python

examples/python-dataflow/webcam_operator.py

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+from enum import Enum
+from typing import Callable
+
+import cv2
+
+
+class DoraStatus(Enum):
+    CONTINUE = 0
+    STOP = 1
+
+
+class Operator:
+    """
+    Example operator incrementing a counter every times its been called.
+
+    The current value of the counter is sent back to dora on `counter`.
+    """
+
+    def __init__(self):
+        self.video_capture = cv2.VideoCapture(0)
+
+    def on_input(
+        self,
+        input_id: str,
+        value: bytes,
+        send_output: Callable[[str, bytes], None],
+    ) -> DoraStatus:
+        """Handle input by incrementing count by one.
+
+        Args:
+            input_id (str): Id of the input declared in the yaml configuration
+            value (bytes): Bytes message of the input
+            send_output (Callable[[str, bytes]]): Function enabling sending output back to dora.
+        """
+
+        ret, frame = self.video_capture.read()
+        if ret:
+            send_output("image", frame.tobytes())
+        else:
+            print("did not sent video")
+
+        return DoraStatus.CONTINUE
+
+    def drop_operator(self):
+        self.video_capture.release()