Adding Chapter 3 files

Chapter3/classes/carexample5.py

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+#carexample5.py
+class Car:
+    c_mileage_units = "Mi"
+    __max_speed = 200
+
+    def __init__(self, color, miles, model):
+        self.i_color = color
+        self.i_mileage = miles
+        self.__no_doors = 4
+        self._model = model
+
+    def __str__(self):
+        return f"car with color {self.i_color}, mileage {self.i_mileage}, model {self._model} and doors {self.__doors()}"
+
+    def __doors(self):
+        return self.__no_doors
+
+if __name__ == "__main__":
+    car = Car ("blue", 1000, "Camry")
+    print (car)
+
+    """These lines are only for illustration and not best practice"""
+    print(Car._Car__max_speed)
+    print (car._Car__doors())
+    print (car._model)         #possible but against the protected definition