PostHog feature flags for Python

Reference files

• references/python.md

  - Python feature flags installation - docs

• references/adding-feature-flag-code.md

  - Adding feature flag code - docs

• references/best-practices.md

  - Feature flag best practices - docs

Key principles

• Environment variables: Always use environment variables for PostHog keys. Never hardcode them.
• Minimal changes: Add feature flag code alongside existing logic. Don't replace or restructure existing code.
• Boolean flags first: Default to boolean flag checks unless the user specifically asks for multivariate flags.
• Server-side when possible: Prefer server-side flag evaluation to avoid UI flicker.

PostHog MCP tools

Framework guidelines

• 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