Bug: AttributeError when instantiating Vehicle in parking_lot.py and missing Enum import in parking_lot.ipynb

Expected Behavior

• Instantiating any vehicle (Motorcycle, Car, or Bus) from solutions/object_oriented_design/parking_lot/parking_lot.py should properly set self.spot_size.
• Running the solution code cell in solutions/object_oriented_design/parking_lot/parking_lot.ipynb should execute cleanly without import errors.

Actual Behavior

1. AttributeError in parking_lot.py (Line 17): Calling Motorcycle('ABC') immediately raises:
   复制

   Traceback (most recent call last):
     File "solutions/object_oriented_design/parking_lot/parking_lot.py", line 17, in __init__
       self.spot_size
   AttributeError: 'Motorcycle' object has no attribute 'spot_size'