python-dataflow-builder

Python Dataflow Builder - Simple Example

This example demonstrates how to use Dora's Python API to build a simple computer vision dataflow that performs real-time object detection using YOLO.

Overview

The simple_example.py script creates a three-node dataflow:

1. Camera Node - Captures video frames from the default camera
2. Object Detection Node - Performs YOLO-based object detection on the frames
3. Plot Node - Visualizes the detected objects by drawing bounding boxes on the frames

What it does

The dataflow:

• Captures 640x480 video frames from camera at 50 FPS (every 20ms)
• Runs YOLO object detection on each frame
• Displays the results with bounding boxes overlaid on the original video

Dependencies

The script automatically installs the following packages:

• opencv-video-capture - For camera input
• dora-yolo - For YOLO object detection
• opencv-plot - For visualization

Key API Methods

add_input(name, source)

Defines an input port for a node. The input can come from:

• Timer source: "dora/timer/millis/20" creates a timer that ticks every 20ms
• Another node's output: Use the output object returned by add_output()

Examples from the code:

# Timer input - triggers camera capture every 20ms
camera.add_input("tick", "dora/timer/millis/20")

# Node-to-node connection - object detection receives images from camera
object_detection.add_input("image", camera_image)

# Multiple inputs - plot receives both images and bounding boxes
plot.add_input("image", camera_image)
plot.add_input("boxes2d", bbox_output)

add_output(name)

Defines an output port for a node and returns an output object that can be used as input for other nodes.

Examples from the code:

# Camera outputs images
camera_image = camera.add_output("image")

# Object detection outputs bounding boxes
bbox_output = object_detection.add_output("bbox")

The returned output objects (camera_image, bbox_output) are then used to connect nodes together by passing them to add_input() on other nodes.

Usage

Run the example:

python simple_example.py

To skip the build (useful for testing YAML generation only):

NO_BUILD=1 python simple_example.py

Generated Files

• dataflow.yml - The generated dataflow configuration file that can be run with dora run