Exercise 3.1
Overview
In section 2, you wrote a program called report.py that printed out
a report showing the performance of a stock portfolio. This program
consisted of some functions. For example:
# report.py
import csv
def read_portfolio(filename):
'''
Read a stock portfolio file into a list of dictionaries with keys
name, shares, and price.
'''
portfolio = []
f = open(filename)
f_csv = csv.reader(f)
headers = next(f_csv)
for row in f_csv:
record = dict(zip(headers, row))
stock = {
'name' : record['name'],
'shares' : int(record['shares']),
'price' : float(record['price'])
}
portfolio.append(stock)
f.close()
return portfolio
...
However, there were also portions of the program that just performed a series of scripted calculations. This code appeared near the end of the program. For example:
...
# Output the report
headers = ('Name', 'Shares', 'Price', 'Change')
print '%10s %10s %10s %10s' % headers
print ('-' * 10 + ' ') * len(headers)
for row in report:
print '%10s %10d %10.2f %10.2f' % row
...
In this exercise, we’re going take this program and organize it a little more strongly around the use of functions.
(a) Structuring a program as a collection of functions
Modify your report.py program so that all major operations, including calculations and output, are carried out by a
collection of functions. Specifically:
-
Create a function
print_report(report)that prints out the report. -
Change the last part of the program so that it is nothing more than a series of function calls and no other computation.
(b) Creating a function for program execution
Take the last part of your program and package it into a single function portfolio_report(portfolio_filename, prices_filename). Have the function work so that
the following function call creates the report as before:
portfolio_report('Data/portfolio.csv', 'Data/prices.csv')
In this final version, your program will be nothing more than a series of function definitions followed by a single function
call to portfolio_report() at the very end (which executes all of the steps involved in the program).
By turning your program into a single function, it becomes easy to run it on different inputs. For example, try these statements interactively after running your program:
>>> portfolio_report('Data/portfolio2.csv', 'Data/prices.csv')
... look at the output ...
>>> files = ['Data/portfolio.csv', 'Data/portfolio2.csv']
>>> for name in files:
print format(name,'-^43s')
portfolio_report(name, 'Data/prices.csv')
print
... look at the output ...
>>>