Parse real-time vehicle positions¶

In the previous section, you made a request to the STM API for Realtime transit data. Now let's parse it into something you can use.

The code¶

Create a file called parse_positions.py and add the following code:

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import os
import requests
from google.transit import gtfs_realtime_pb2

URL = "https://api.stm.info/pub/od/gtfs-rt/ic/v2/vehiclePositions"
headers = {
    "accept": "application/x-protobuf",
    "apiKey": os.environ["STM_API_KEY"],
}

response = requests.get(URL, headers=headers)

feed = gtfs_realtime_pb2.FeedMessage()
feed.ParseFromString(response.content)

for entity in feed.entity:
    if entity.HasField("vehicle"):
        vehicle = entity.vehicle
        position = vehicle.position
        print(
            f"Vehicle {vehicle.vehicle.id}: "
            f"lat={position.latitude}, "
            f"lon={position.longitude}, "
            f"speed={position.speed}"
        )

• Lines 1-3: Import required modules (os, requests, and gtfs_realtime_pb2)
• Line 5: Define the API endpoint URL. This is the same Vehicle Positions endpoint from the previous section and can be found in the STM developer portal.
• Lines 6-9: Create headers dictionary with accept header and the API key loaded from the environment variable
• Line 11: Make GET request to the endpoint using requests
• Lines 13-14: Create an empty FeedMessage and parse the binary response into it. A GTFS Realtime feed is a FeedMessage containing a list of entity records. Each entity can represent different things — a vehicle position, a trip update, or a service alert.
• Line 17: Before accessing entity.vehicle (the VehiclePosition), the code checks HasField("vehicle") to make sure this entity actually carries a vehicle position.
• Lines 18-25: Each vehicle entity carries a VehiclePosition. Its vehicle field is a VehicleDescriptor with the bus's id — so vehicle.vehicle.id is the bus number. The position field holds lat/lon/speed.

Run it¶

python parse_positions.py

You should see output like:

Vehicle 80012: lat=45.510, lon=-73.564, speed=14.0
Vehicle 80014: lat=45.522, lon=-73.578, speed=0.0
...

Congratulations, you've parsed your first GTFS Realtime feed! Next, you'll build an interactive dashboard to visualize these vehicle positions on a map.