GTFS Realtime Python Bindings

Warnings

• breaking The `gtfs-realtime-bindings` library relies on the underlying `protobuf` library. Future major versions of `protobuf` (e.g., beyond 5.0) may introduce breaking changes or require specific versions for optimal compatibility, potentially leading to parsing errors if `protobuf` is not correctly managed.
  Fix: Ensure your `protobuf` installation is compatible with the `gtfs-realtime-bindings` version. Regularly check the project's GitHub issues for reported `protobuf` compatibility problems and upgrade your `protobuf` library as recommended by the `gtfs-realtime-bindings` project.
• gotcha Protocol Buffers distinguish between a field explicitly set to its default value (e.g., 0 for an integer) and a field that is entirely unset. Directly accessing fields without checking for their presence using the `HasField()` method can lead to misinterpretation, as an unset field will return its default value in Python, which might not be the intended semantic zero or empty string.
  Fix: Always use `if entity.HasField('field_name'):` before attempting to access the value of an optional field to ensure it was present in the original data stream.
• gotcha The `gtfs-realtime-bindings` library is generated from the `gtfs-realtime.proto` specification. The GTFS Realtime specification itself evolves, introducing new fields, deprecating old ones, or clarifying semantics (e.g., GTFS-realtime v2.0 spec). Using older bindings with newer feeds (or vice-versa) may result in parsing issues or incorrect interpretation of data, particularly with experimental features or required field changes.
  Fix: Keep your `gtfs-realtime-bindings` library updated to the latest version to ensure compatibility with the most recent `gtfs-realtime.proto` specification. If working with feeds that use experimental features, be aware that these may change or be removed in future spec updates.
• gotcha The GTFS Realtime specification provides guidelines on data freshness. Specifically, Trip Updates and Vehicle Positions should generally not be older than 90 seconds, and Service Alerts not older than 10 minutes. Consuming stale data, even if successfully parsed, can lead to inaccurate real-time information for end-users.
  Fix: Implement checks on the `FeedHeader.timestamp` to ensure the data being processed is within acceptable freshness thresholds. Contact the data producer if feeds are consistently stale.

Install

• pip install gtfs-realtime-bindings Install latest version

Imports

• gtfs_realtime_pb2

  from google.transit import gtfs_realtime_pb2

  This module contains the generated Python classes for GTFS-realtime messages, such as FeedMessage, TripUpdate, and VehiclePosition.

Quickstart

This quickstart demonstrates how to fetch a GTFS-realtime feed from a URL, parse its binary content into a `FeedMessage` object, and iterate through its entities to print basic information about trip updates, vehicle positions, or service alerts. It uses the `requests` library for fetching the data, which is a common pattern for consuming GTFS-realtime feeds.

import requests
from google.transit import gtfs_realtime_pb2
import os

# Replace with the actual URL of your GTFS-realtime data feed
GTFS_REALTIME_FEED_URL = os.environ.get('GTFS_REALTIME_FEED_URL', 'https://gtfs.example.com/realtime-feed.pb')

# Optional: If your API requires an API key in headers
API_KEY = os.environ.get('GTFS_REALTIME_API_KEY', '')
headers = {'x-api-key': API_KEY} if API_KEY else {}

try:
    response = requests.get(GTFS_REALTIME_FEED_URL, headers=headers, timeout=10)
    response.raise_for_status()  # Raise an exception for HTTP errors

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

    print(f"Successfully parsed feed from {GTFS_REALTIME_FEED_URL}")
    print(f"Feed header timestamp: {feed.header.timestamp}")
    print(f"Number of entities: {len(feed.entity)}")

    for entity in feed.entity:
        if entity.HasField('trip_update'):
            print(f"  Trip Update: {entity.trip_update.trip.trip_id}")
            # Example of accessing a field, always check HasField() first
            if entity.trip_update.trip.HasField('route_id'):
                print(f"    Route ID: {entity.trip_update.trip.route_id}")
        elif entity.HasField('vehicle'):
            print(f"  Vehicle Position: {entity.vehicle.trip.trip_id}")
            if entity.vehicle.HasField('position'):
                print(f"    Lat: {entity.vehicle.position.latitude}, Lon: {entity.vehicle.position.longitude}")
        elif entity.HasField('alert'):
            print(f"  Service Alert: {entity.alert.header_text.translation[0].text if entity.alert.header_text.translation else 'N/A'}")

except requests.exceptions.RequestException as e:
    print(f"Error fetching GTFS-realtime feed: {e}")
except Exception as e:
    print(f"Error parsing GTFS-realtime feed: {e}")