Script that uses the PostHog Python SDK to call feature flags

ff_script.py

import os
import json
import backoff
import logging
from posthog import Posthog

# SingletonMeta implementation
class SingletonMeta(type):
    _instances = {}
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(SingletonMeta, cls).__call__(*args, **kwargs)
        return cls._instances[cls]

# Set up logging
logger = logging.getLogger(__name__)
logging.basicConfig(level=logging.INFO)

class PosthogClient(metaclass=SingletonMeta):
    _posthog: Posthog

    def __init__(self):
        api_key = os.environ.get("POSTHOG_API_KEY", "")
        host = os.environ.get("POSTHOG_HOST", "https://us.posthog.com")
        if not api_key or not host:
            raise ValueError("Posthog API key or host not found")

        self._posthog = Posthog(api_key, host, debug=True)

    @backoff.on_exception(backoff.expo, Exception, max_time=7, raise_on_giveup=True)
    def get_feature_flag(self, feature_flag_key, distinct_id):
        example_variant = self._posthog.get_feature_flag(key=feature_flag_key, distinct_id=distinct_id)
        logger.info(f"Feature flag value: {example_variant}")
        return example_variant

    @backoff.on_exception(backoff.expo, Exception, max_tries=2, raise_on_giveup=True)
    def get_feature_flag_payload(
        self, feature_flag_key, distinct_id, payload_key=None
    ):
        payload = self._posthog.get_feature_flag_payload(
            key=feature_flag_key, distinct_id=distinct_id
        )
        logger.info(f"Feature flag payload: {payload}")
        if payload:
            if not payload_key:
                return payload

            try:
                payload = json.loads(payload)
                return payload.get(payload_key)
            except json.JSONDecodeError:
                logger.error(
                    "Failed to parse feature flag payload",
                    extra={
                        "feature flag": feature_flag_key,
                        "user id": distinct_id,
                        "payload": payload,
                        "payload key": payload_key,
                    },
                )
        return None

def main():
    # Prompt for PostHog API key and host if not set in environment variables
    api_key = os.environ.get("POSTHOG_API_KEY")
    if not api_key:
        api_key = input("Enter your PostHog API Key: ")
        os.environ["POSTHOG_API_KEY"] = api_key

    host = os.environ.get("POSTHOG_HOST")
    if not host:
        host = input("Enter your PostHog Host (e.g., https://app.posthog.com): ")
        os.environ["POSTHOG_HOST"] = host

    # Create an instance of PosthogClient
    client = PosthogClient()

    # Prompt for feature flag key and user ID
    feature_flag_key = input("Enter feature flag key: ")
    distinct_id = input("Enter user ID: ")

    # Get feature flag value
    try:
        flag_value = client.get_feature_flag(feature_flag_key, distinct_id)
        print(f"Feature flag '{feature_flag_key}' value for user '{distinct_id}': {flag_value}")
    except Exception as e:
        print(f"Error getting feature flag: {e}")

    # Get feature flag payload
    try:
        payload = client.get_feature_flag_payload(feature_flag_key, distinct_id)
        print(f"Feature flag payload for '{feature_flag_key}' and user '{distinct_id}': {payload}")
    except Exception as e:
        print(f"Error getting feature flag payload: {e}")

if __name__ == "__main__":
    main()