Adding Chapter 3 files

Chapter3/classes/carwithInnerexample1.py

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+#carwithinnerexample1.py
+class Car:
+    """outer class"""
+    c_mileage_units = "Mi"
+    def __init__(self, color, miles, eng_size):
+        self.i_color = color
+        self.i_mileage = miles
+        self.i_engine = self.Engine(eng_size)
+
+    def __str__(self):
+        return f"car with color {self.i_color}, mileage {self.i_mileage} and engine of {self.i_engine}"
+
+    class Engine:
+        """inner class"""
+        def __init__(self, size):
+            self.i_size = size
+
+        def __str__(self):
+            return self.i_size
+
+
+if __name__ == "__main__":
+    car = Car ("blue", 1000, "2.5L")
+    print (car)
+    print (car.i_engine.i_size)