Flask

Application Context

• current_app only works inside request or with app.app_context() — "working outside application context" error
• g is per-request storage — lost after request ends, use for db connections
• Background tasks need context — with app.app_context(): or pass data, not proxies
• create_app() factory pattern avoids circular imports — import current_app not app

Request Context

• request, session only inside request — "working outside request context" error
• url_for needs context — url_for('static', filename='x', _external=True) for absolute URLs
• Test client provides context automatically — but manual context for non-request code

Circular Imports

• from app import app in models causes circular — use factory pattern
• Import inside function for late binding — or use current_app
• Blueprints help organize — register at factory time, not import time
• Extensions init with init_app(app) pattern — create without app, bind later