Integration Fastapi

The example project shows the target implementation pattern. Consult the documentation for API details.

Key principles

• Environment variables: Always use environment variables for PostHog keys. Never hardcode them.
• Minimal changes: Add PostHog code alongside existing integrations. Don't replace or restructure existing code.
• Match the example: Your implementation should follow the example project's patterns as closely as possible.

Framework guidelines

• Initialize PostHog in the lifespan context manager on startup using posthog.api_key and posthog.host
• Call posthog.flush() in the lifespan shutdown to ensure all events are sent before the app exits
• Use Pydantic Settings with @lru_cache decorator on get_settings() for caching and easy test overrides
• Use FastAPI dependency injection (Depends) for accessing current_user and settings in route handlers
• Use the same context API pattern as Flask/Django (with new_context(), identify_context(user_id), then capture())
• Remember that source code is available in the venv/site-packages directory
• posthog is the Python SDK package name
• Install dependencies with pip install posthog or pip install -r requirements.txt and do NOT use unquoted version specifiers like >= directly in shell commands
• In CLIs and scripts: MUST call posthog.shutdown() before exit or all events are lost

Identifying users

Identify users during login and signup events. Refer to the example code and documentation for the correct identify pattern for this framework. If both frontend and backend code exist, pass the client-side session and distinct ID using X-POSTHOG-DISTINCT-ID and X-POSTHOG-SESSION-ID headers to maintain correlation.

Error tracking

Add PostHog error tracking to relevant files, particularly around critical user flows and API boundaries.