OOP and Design patterns Exercises
1. (20 min) The graph module (provided on the Wiki page) contains a set
of classes for representing graphs. On a piece of paper reverse engineer its
design:
(a) Write down all class names, their methods and public properties; try
to understand what all of them do.
(b) Figure out how different classes are depending on each other.
(c) Use the classes to represent the following graph:
(d) What are the weaknesses of this design? The code contains comments
that raise some questions about the design, think about these.
(e) How would you improve this design? How might an alternative design
look like? We will come back to this later, so don’t spend too much
time on it now.
2. (40 min) Modify the code in starbuzz.py to use the Decorator Pattern.
(a) Define a class BeverageDecorator which is instantiated with a bev-
erage object and contains two methods: get cost which adds the
cost of the decorator to the total drink cost and get description
which updates the description of the drink.
(b) Subclassing BeverageDecorator define new ingredients: Milk and
Cream. Use the ingridients to produce new drinks combinations.
(c) (Optional ) Write unittests for your code and add propper docstrings.
3. (30 min) Implement a Python iterator which iterates over string characters
(ASCII only) returning their ASCII code (obtained by ord function):
(a) Define a new iterator class which contains two methods:
•init – a constructor taking the ASCII string as a argument,
•next – returns the ASCII code of the next character or raises a
StopIteration exception if the string end was encountered.
(b) Define a new iterable class which wraps around a string and contains
iter method which returns the iterator instance.
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