Adding Chapter 3 files

Chapter3/classes/carexample4.py

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+#carexampl4.py
+class Car:
+    c_mileage_units = "Mi"
+    def __init__(self, color, miles):
+        self.i_color = color
+        self.i_mileage = miles
+
+    def __str__(self):
+        return f"car with color {self.i_color} and mileage {self.i_mileage}"
+
+if __name__ == "__main__":
+    car1 = Car ("blue", 1000)
+    print (str(car1))
+    print(repr(car1))
+    print(dir(car1))