coding-mentor-agent/kb/python-course-kb-practical-python/wiki/exercises/7-11-class-methods-in-practice.md

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id	source_exercise_id	title	section	source_path	source_repo	source_commit	student_visible_solution	has_private_solution	skip
practical-python-7.11	7.11	Class Methods in Practice	7.5 Decorated Methods	07_Advanced_Topics/05_Decorated_methods.md	https://github.com/dabeaz-course/practical-python	93dca856b41c61a0a0f85ae334116e4c125629ea	false	true	false

Exercise 7.11: Class Methods in Practice

Source: Practical Python Programming, 07_Advanced_Topics/05_Decorated_methods.md.

Exercise 7.11: Class Methods in Practice

In your report.py and portfolio.py files, the creation of a Portfolio object is a bit muddled. For example, the report.py program has code like this:

def read_portfolio(filename, **opts):
    '''
    Read a stock portfolio file into a list of dictionaries with keys
    name, shares, and price.
    '''
    with open(filename) as lines:
        portdicts = fileparse.parse_csv(lines,
                                        select=['name','shares','price'],
                                        types=[str,int,float],
                                        **opts)

    portfolio = [ Stock(**d) for d in portdicts ]
    return Portfolio(portfolio)

and the portfolio.py file defines Portfolio() with an odd initializer like this:

class Portfolio:
    def __init__(self, holdings):
        self.holdings = holdings
    ...

Frankly, the chain of responsibility is all a bit confusing because the code is scattered. If a Portfolio class is supposed to contain a list of Stock instances, maybe you should change the class to be a bit more clear. Like this:

# portfolio.py

import stock

class Portfolio:
    def __init__(self):
        self.holdings = []

    def append(self, holding):
        if not isinstance(holding, stock.Stock):
            raise TypeError('Expected a Stock instance')
        self.holdings.append(holding)
    ...

If you want to read a portfolio from a CSV file, maybe you should make a class method for it:

# portfolio.py

import fileparse
import stock

class Portfolio:
    def __init__(self):
        self.holdings = []

    def append(self, holding):
        if not isinstance(holding, stock.Stock):
            raise TypeError('Expected a Stock instance')
        self.holdings.append(holding)

    @classmethod
    def from_csv(cls, lines, **opts):
        self = cls()
        portdicts = fileparse.parse_csv(lines,
                                        select=['name','shares','price'],
                                        types=[str,int,float],
                                        **opts)

        for d in portdicts:
            self.append(stock.Stock(**d))

        return self

To use this new Portfolio class, you can now write code like this:

>>> from portfolio import Portfolio
>>> with open('Data/portfolio.csv') as lines:
...     port = Portfolio.from_csv(lines)
...
>>>

Make these changes to the Portfolio class and modify the report.py code to use the class method.

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关联来源

• summaries/05_Decorated_methods