Great question! Let’s break down the differences first, then fix your Redis session persistence issue.

First, what each method actually does:

• session.pop(key): Removes a single key-value pair from the current session. For example, session.pop('user_id') would delete just the user ID entry while leaving other session data (like saved preferences) intact. The session itself—and its corresponding Redis record—stays active.
• session.clear(): Wipes all key-value pairs from the session, but does not delete the session’s entry in Redis. The Redis key (usually formatted as session:<session_id>) remains, but its value becomes an empty dictionary. This is exactly why you’re still seeing the session in Redis after calling it.

To fully terminate the current session and delete its Redis storage, you’ll need a multi-step workflow—neither pop() nor clear() alone will do this. Here’s the best practice:

1. Clear residual session data (optional but clean):

   session.clear()
   

   This ensures no leftover data remains before we delete the session entirely.

2. Delete the session from Redis:
   You’ll need your Redis client instance and the current session ID (available via session.sid). Flask-Session uses a default key prefix of session:, so we’ll use that to target the correct Redis entry:

   from flask import session
   # Replace with your app's configured Redis client
   from your_app import redis_client
   
   session_id = session.sid
   redis_client.delete(f"session:{session_id}")
   

3. Invalidate the client-side cookie:
   Even after deleting the session from Redis, the client might still hold the old session ID cookie. To prevent reuse, expire the cookie in your response:

   from flask import make_response
   
   response = make_response("Session terminated successfully")
   # Match this to your app's SESSION_COOKIE_NAME (default is "session")
   response.set_cookie("session", expires=0)
   return response
   

• Use session.pop(key) when you only need to remove specific session data (e.g., logging out a user but keeping their theme setting).
• Use session.clear() when you want to reset all session data but keep the session alive (e.g., resetting a form’s state).
• Use the full workflow above when you need to completely kill the session (e.g., user logout, security-focused session invalidation).

内容的提问来源于stack exchange，提问作者Peresh Cheng