coding-mentor-agent/kb/python-course-kb-practical-python/wiki/exercises/2-4-a-list-of-tuples.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-2.4	2.4	A list of tuples	2.2 Containers	02_Working_with_data/02_Containers.md	https://github.com/dabeaz-course/practical-python	93dca856b41c61a0a0f85ae334116e4c125629ea	false	false	false

Exercise 2.4: A list of tuples

Source: Practical Python Programming, 02_Working_with_data/02_Containers.md.

Exercise 2.4: A list of tuples

The file Data/portfolio.csv contains a list of stocks in a portfolio. In Exercise 1.30, you wrote a function portfolio_cost(filename) that read this file and performed a simple calculation.

Your code should have looked something like this:

# pcost.py

import csv

def portfolio_cost(filename):
    '''Computes the total cost (shares*price) of a portfolio file'''
    total_cost = 0.0

    with open(filename, 'rt') as f:
        rows = csv.reader(f)
        headers = next(rows)
        for row in rows:
            nshares = int(row[1])
            price = float(row[2])
            total_cost += nshares * price
    return total_cost

Using this code as a rough guide, create a new file report.py. In that file, define a function read_portfolio(filename) that opens a given portfolio file and reads it into a list of tuples. To do this, you’re going to make a few minor modifications to the above code.

First, instead of defining total_cost = 0, you’ll make a variable that’s initially set to an empty list. For example:

portfolio = []

Next, instead of totaling up the cost, you’ll turn each row into a tuple exactly as you just did in the last exercise and append it to this list. For example:

for row in rows:
    holding = (row[0], int(row[1]), float(row[2]))
    portfolio.append(holding)

Finally, you’ll return the resulting portfolio list.

Experiment with your function interactively (just a reminder that in order to do this, you first have to run the report.py program in the interpreter):

Hint: Use -i when executing the file in the terminal

>>> portfolio = read_portfolio('Data/portfolio.csv')
>>> portfolio
[('AA', 100, 32.2), ('IBM', 50, 91.1), ('CAT', 150, 83.44), ('MSFT', 200, 51.23),
    ('GE', 95, 40.37), ('MSFT', 50, 65.1), ('IBM', 100, 70.44)]
>>>
>>> portfolio[0]
('AA', 100, 32.2)
>>> portfolio[1]
('IBM', 50, 91.1)
>>> portfolio[1][1]
50
>>> total = 0.0
>>> for s in portfolio:
        total += s[1] * s[2]

>>> print(total)
44671.15
>>>

This list of tuples that you have created is very similar to a 2-D array. For example, you can access a specific column and row using a lookup such as portfolio[row][column] where row and column are integers.

That said, you can also rewrite the last for-loop using a statement like this:

>>> total = 0.0
>>> for name, shares, price in portfolio:
            total += shares*price

>>> print(total)
44671.15
>>>

关联来源

• summaries/02_Containers