[ Index | Exercise 1.3 | Exercise 1.5 ]
Objectives:
- Review of how to define simple functions
- Exception handling
Files Created: None
Files Modified: pcost.py
Take the program pcost.py that you wrote in the last exercise and
convert it into a function portfolio_cost(filename) that takes a
filename as input, reads the portfolio data in that file, and returns
the total cost of the portfolio as a floating point number. Once you
written the function, have your program call the function by simply
adding this statement at the end:
print(portfolio_cost('Data/portfolio.dat'))Run your program and make sure it produces the same output as before.
When writing programs that process data, it is common to encounter
errors related to bad data (malformed, missing fields, etc.). Modify
your pcost.py program to read the data file Data/portfolio3.dat
and run it (hint: it should crash).
Modify your function slightly so that it is able to recover from lines
with bad data. For example, the conversion functions int() and
float() raise a ValueError exception if they can't convert the
input. Use try and except to catch and print a warning message
about lines that can't be parsed. For example:
Couldn't parse: 'C - 53.08\n'
Reason: invalid literal for int() with base 10: '-'
Couldn't parse: 'DIS - 34.20\n'
Reason: invalid literal for int() with base 10: '-'
...
Try running your program on the Data/portfolio3.dat file
again. It should run successfully despite printed warning messages.
Run your pcost.py program and call the
portfolio_cost() function directly from the interactive
interpreter.
>>> portfolio_cost('Data/portfolio.dat')
44671.15
>>> portfolio_cost('Data/portfolio2.dat')
19908.75
>>>Note: To do this, you might have to run python using the -i
option. For example:
bash % python3 -i pcost.py
We are going to be writing a lot of programs where you define functions and experiment interactively. Make sure you know how to do this.
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