PostHog integration for Flask

Workflow

1. basic-integration-1.0-begin.md

   - PostHog Setup - Begin ← Start here

2. basic-integration-1.1-edit.md

   - PostHog Setup - Edit

3. basic-integration-1.2-revise.md

   - PostHog Setup - Revise

4. basic-integration-1.3-conclude.md

   - PostHog Setup - Conclusion

Reference files

• references/EXAMPLE.md

  - Flask example project code

• references/flask.md

  - Flask - docs

• references/identify-users.md

  - Identify users - docs

• references/basic-integration-1.0-begin.md

  - PostHog setup - begin

• references/basic-integration-1.1-edit.md

  - PostHog setup - edit

• references/basic-integration-1.2-revise.md

  - PostHog setup - revise

• references/basic-integration-1.3-conclude.md

  - PostHog setup - conclusion

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 globally in create_app() using posthog.api_key and posthog.host (NOT per-request)
• Manually capture exceptions with

  posthog.capture_exception(e)

  for error tracking since Flask has built-in error handlers
• Blueprint registration happens AFTER PostHog initialization in create_app()
• 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
• Always use the Posthog() class constructor (instance-based API) instead of module-level posthog.api_key config
• Always include enable_exception_autocapture=True in the Posthog() constructor to automatically track exceptions
• NEVER send PII in capture() event properties — no emails, full names, phone numbers, physical addresses, IP addresses, or user-generated content
• PII belongs in identify() person properties, NOT in capture() event properties. Safe event properties are metadata like message_length, form_type, boolean flags.
• Register posthog_client.shutdown with atexit.register() to ensure all events are flushed on exit
• The Python SDK has NO identify() method — use posthog_client.set(distinct_id=user_id, properties={...}) to set person properties, or use identify_context(user_id) within a context

Identifying users

X-POSTHOG-DISTINCT-ID

X-POSTHOG-SESSION-ID

Error tracking