renumbering chapters >= 19

23-descriptor/bulkfood/model_v4c.py

@@ -0,0 +1,13 @@
+# BEGIN MODEL_V4
+class Quantity:
+
+    def __set_name__(self, owner, name):  # <1>
+        self.storage_name = name          # <2>
+
+    def __set__(self, instance, value):   # <3>
+        if value > 0:
+            instance.__dict__[self.storage_name] = value
+        else:
+            msg = f'{self.storage_name} must be > 0'
+            raise ValueError(msg)
+# END MODEL_V4