Added more test files from lectures.

test20.py

@@ -0,0 +1,33 @@
+class Menu:
+    hotdog = 10
+    hamburger = 10
+
+    def __init__(self) -> None:
+        self.hotdog = 10
+        self.hamburger = 10
+
+
+class SlotsMenu:
+    __slots__ = ('hotdog', 'hamburger', 'cheeseburger')
+
+    def __init__(self) -> None:
+        self.hotdog = 10
+        self.hamburger = 10
+
+    def __get__(self, instance):
+        print(f"DEBUG: looked up {instance}")
+
+if __name__ == '__main__':
+    menu = Menu()
+
+    print(f"cost of hamburger = {menu.hamburger}")
+    menu.__dict__['hamburger'] = 1
+    print(f"new cost of hamburger = {menu.hamburger}")
+
+    slotsmenu = SlotsMenu()
+
+    print(f"cost of hamburger = {slotsmenu.hamburger}")
+    slotsmenu.cheeseburger = 1
+    print(f"cost of cheeseburger: {slotsmenu.cheeseburger=}")
+    #slotsmenu.__dict__['hamburger'] = 1
+    print(f"new cost of hamburger = {slotsmenu.hamburger}")