Add the User.timezone property

It either queries the user’s `timezone` setting, uses the app’s default time zone (stored in the
`DEFAULT_TIMEZONE` configuration key), or uses UTC as a final fallback.

calsocial/models.py

@@ -18,6 +18,7 @@
 """
 
 from datetime import datetime
+from warnings import warn
 
 from flask_security import UserMixin, RoleMixin
 from flask_sqlalchemy import SQLAlchemy
@@ -107,6 +108,23 @@ class User(db.Model, UserMixin):
 
         return proxy
 
+    @property
+    def timezone(self):
+        from flask import current_app
+        from pytz import timezone, UTC
+        from pytz.exceptions import UnknownTimeZoneError
+
+        timezone_str = self.settings['timezone']
+
+        if not timezone_str:
+            timezone_str = current_app.settings.get('DEFAULT_TIMEZONE', 'UTC')
+
+        try:
+            return timezone(timezone_str)
+        except pytz.exceptions.UnknownTimeZoneError:
+            warn(f'Timezone of {user} (or the default timezone) "{timezone_str}" is invalid')
+            return UTC
+
     def __repr__(self):
         return f'<User {self.id}({self.username})>'