O365 is a Python client library for the Microsoft Graph API, providing object-oriented wrappers for Outlook/Office 365 services including email, calendar, contacts, OneDrive, Teams, SharePoint, tasks, planner, groups, directory, Excel, and webhook subscriptions. The library handles OAuth2 authentication via MSAL with pluggable token backends (filesystem, AWS S3, Firestore, Django, etc.), automatic token refresh, and pagination. Its architecture centers on an ApiComponent base class that all resource objects inherit from, a Connection class for HTTP and OAuth flow, and a Protocol abstraction for API versioning. Key entry points include the Account facade (which provides access to all services) and lower-level classes like Connection, Message, MailBox, Calendar, Drive, and Teams. External dependencies include requests, msal, beautifulsoup4, python-dateutil, tzlocal, and tzdata. The library is designed for developers integrating Microsoft 365 data into Python applications, scripts, or web frameworks like Flask.