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id, source_exercise_id, title, section, source_path, source_repo, source_commit, student_visible_solution, has_private_solution, skip
| id | source_exercise_id | title | section | source_path | source_repo | source_commit | student_visible_solution | has_private_solution | skip |
|---|---|---|---|---|---|---|---|---|---|
| practical-python-4.8 | 4.8 | Putting it all together | 4.2 Inheritance | 04_Classes_objects/02_Inheritance.md | https://github.com/dabeaz-course/practical-python | 93dca856b41c61a0a0f85ae334116e4c125629ea | false | false | false |
Exercise 4.8: Putting it all together
Source: Practical Python Programming,
04_Classes_objects/02_Inheritance.md.
Exercise 4.8: Putting it all together
Modify the report.py program so that the portfolio_report() function takes
an optional argument specifying the output format. For example:
>>> report.portfolio_report('Data/portfolio.csv', 'Data/prices.csv', 'txt')
Name Shares Price Change
---------- ---------- ---------- ----------
AA 100 9.22 -22.98
IBM 50 106.28 15.18
CAT 150 35.46 -47.98
MSFT 200 20.89 -30.34
GE 95 13.48 -26.89
MSFT 50 20.89 -44.21
IBM 100 106.28 35.84
>>>
Modify the main program so that a format can be given on the command line:
bash $ python3 report.py Data/portfolio.csv Data/prices.csv csv
Name,Shares,Price,Change
AA,100,9.22,-22.98
IBM,50,106.28,15.18
CAT,150,35.46,-47.98
MSFT,200,20.89,-30.34
GE,95,13.48,-26.89
MSFT,50,20.89,-44.21
IBM,100,106.28,35.84
bash $
Discussion
Writing extensible code is one of the most common uses of inheritance in libraries and frameworks. For example, a framework might instruct you to define your own object that inherits from a provided base class. You're then told to fill in various methods that implement various bits of functionality.
Another somewhat deeper concept is the idea of "owning your abstractions." In the exercises, we defined our own class for formatting a table. You may look at your code and tell yourself "I should just use a formatting library or something that someone else already made instead!" No, you should use BOTH your class and a library. Using your own class promotes loose coupling and is more flexible. As long as your application uses the programming interface of your class, you can change the internal implementation to work in any way that you want. You can write all-custom code. You can use someone's third party package. You swap out one third-party package for a different package when you find a better one. It doesn't matter--none of your application code will break as long as you preserve the interface. That's a powerful idea and it's one of the reasons why you might consider inheritance for something like this.
That said, designing object oriented programs can be extremely difficult. For more information, you should probably look for books on the topic of design patterns (although understanding what happened in this exercise will take you pretty far in terms of using objects in a practically useful way).
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