coding-mentor-agent/kb/python-course-kb-practical-python/wiki/exercises/5-6-simple-properties.md

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-5.6	5.6	Simple Properties	5.2 Classes and Encapsulation	05_Object_model/02_Classes_encapsulation.md	https://github.com/dabeaz-course/practical-python	93dca856b41c61a0a0f85ae334116e4c125629ea	false	false	false

Exercise 5.6: Simple Properties

Source: Practical Python Programming, 05_Object_model/02_Classes_encapsulation.md.

Exercise 5.6: Simple Properties

Properties are a useful way to add "computed attributes" to an object. In stock.py, you created an object Stock. Notice that on your object there is a slight inconsistency in how different kinds of data are extracted:

>>> from stock import Stock
>>> s = Stock('GOOG', 100, 490.1)
>>> s.shares
100
>>> s.price
490.1
>>> s.cost()
49010.0
>>>

Specifically, notice how you have to add the extra () to cost because it is a method.

You can get rid of the extra () on cost() if you turn it into a property. Take your Stock class and modify it so that the cost calculation works like this:

>>> ================================ RESTART ================================
>>> from stock import Stock
>>> s = Stock('GOOG', 100, 490.1)
>>> s.cost
49010.0
>>>

Try calling s.cost() as a function and observe that it doesn't work now that cost has been defined as a property.

>>> s.cost()
... fails ...
>>>

Making this change will likely break your earlier pcost.py program. You might need to go back and get rid of the () on the cost() method.

关联来源

• summaries/02_Classes_encapsulation