Updating the underscore in Python names article (#688)

* Updating the underscore in Python names article

* Post final QA

---------

Co-authored-by: Bartosz Zaczyński <bartosz.zaczynski@gmail.com>

Author: lpozo

python-double-underscore/cart.py

@@ -1,6 +1,5 @@
 class ShoppingCart:
-    def __init__(self, customer_id):
-        self.customer_id = customer_id
+    def __init__(self):
         self.products = []
 
     def add_product(self, product):
@@ -11,5 +10,3 @@ def get_products(self):
 
     def __len__(self):
         return len(self.products)
-
-    # Implementation...

python-double-underscore/csv_data.py

@@ -1,5 +1,3 @@
-# csv_data.py
-
 import csv
 
 

python-double-underscore/mangling.py

@@ -0,0 +1,32 @@
+class A:
+    def __init__(self):
+        self.__attr = 0
+
+    def __method(self):
+        print("A.__attr = ", self.__attr)
+
+
+class B(A):
+    def __init__(self):
+        super().__init__()
+        self.__attr = 1  # Doesn't override A.__attr
+
+    def __method(self):  # Doesn't override A.__method()
+        print("B.__attr = ", self.__attr)
+
+
+if __name__ == "__main__":
+    a = A()
+    b = B()
+
+    # Call the mangled methods
+    print(f"{a._A__method()=}")
+    print(f"{b._B__method()=}")
+
+    # Check attributes
+    print(f"{a.__dict__=}")
+    print(f"{b.__dict__=}")
+
+    # Access the attributes on b
+    print(f"{b._A__attr=}")
+    print(f"{b._B__attr=}")