Rename zerver/lib/session_user.py to sessions.py.

zerver/lib/sessions.py

@@ -0,0 +1,19 @@
+from __future__ import absolute_import
+
+from django.contrib.auth import SESSION_KEY, get_user_model
+from django.contrib.sessions.models import Session
+
+from typing import Mapping, Optional, Text
+
+
+def get_session_dict_user(session_dict):
+    # type: (Mapping[Text, int]) -> Optional[int]
+    # Compare django.contrib.auth._get_user_session_key
+    try:
+        return get_user_model()._meta.pk.to_python(session_dict[SESSION_KEY])
+    except KeyError:
+        return None
+
+def get_session_user(session):
+    # type: (Session) -> int
+    return get_session_dict_user(session.get_decoded())