Fix sorting of shells & users

* The return value didn't sort the shells,
  sorted(shells.list,key=len) does nothing, as the length of each
  tuple is 2: the key & the value, while you obviously wanted the length
  of the user list
* The exercise also requested listing the usernames '(sorted
  alphabetically)'

Author: aelmahmoudy

ch03-lists-tuples/e12b3_shells_and_users.py

@@ -14,4 +14,8 @@ def shells_and_users_by_popularity(filename):
 
         shells[shell].append(username)
 
-    return sorted(shells.items(), key=len)
+    # sort usernames for each shell:
+    for shell in shells:
+        shells[shell] = sorted(shells[shell])
+
+    return {s: shells[s] for s in sorted(shells.keys(), key=lambda s: len(shells[s]), reverse=True)}