88 lines
2.6 KiB
Markdown
88 lines
2.6 KiB
Markdown
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\[ [Index](index.md) | [Exercise 1.3](ex1_3.md) | [Exercise 1.5](ex1_5.md) \]
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# Exercise 1.4
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*Objectives:*
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- Review of how to define simple functions
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- Exception handling
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*Files Created:* None
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*Files Modified:* `pcost.py`
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## (a) Defining a function
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Take the program `pcost.py` that you wrote in the last exercise and
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convert it into a function `portfolio_cost(filename)` that takes a
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filename as input, reads the portfolio data in that file, and returns
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the total cost of the portfolio as a floating point number. Once you
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written the function, have your program call the function by simply
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adding this statement at the end:
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```python
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print(portfolio_cost('Data/portfolio.dat'))
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```
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Run your program and make sure it produces the same output as
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before.
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## (b) Adding Error Handling
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When writing programs that process data, it is common to encounter
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errors related to bad data (malformed, missing fields, etc.). Modify
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your `pcost.py` program to read the data file `Data/portfolio3.dat`
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and run it (hint: it should crash).
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Modify your function slightly so that it is able to recover from lines
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with bad data. For example, the conversion functions `int()` and
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`float()` raise a `ValueError` exception if they can't convert the
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input. Use `try` and `except` to catch and print a warning message
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about lines that can't be parsed. For example:
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```
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Couldn't parse: 'C - 53.08\n'
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Reason: invalid literal for int() with base 10: '-'
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Couldn't parse: 'DIS - 34.20\n'
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Reason: invalid literal for int() with base 10: '-'
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...
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```
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Try running your program on the `Data/portfolio3.dat` file
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again. It should run successfully despite printed warning messages.
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## (c) Interactive Experimentation
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Run your `pcost.py` program and call the
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`portfolio_cost()` function directly from the interactive
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interpreter.
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```python
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>>> portfolio_cost('Data/portfolio.dat')
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44671.15
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>>> portfolio_cost('Data/portfolio2.dat')
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19908.75
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>>>
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```
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Note: To do this, you might have to run python using the `-i`
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option. For example:
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```
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bash % python3 -i pcost.py
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```
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We are going to be writing a lot of programs where you define
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functions and experiment interactively. Make sure you know how to do
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this.
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\[ [Solution](soln1_4.md) | [Index](index.md) | [Exercise 1.3](ex1_3.md) | [Exercise 1.5](ex1_5.md) \]
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----
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`>>>` Advanced Python Mastery
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`...` A course by [dabeaz](https://www.dabeaz.com)
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`...` Copyright 2007-2023
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. This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0 International License](http://creativecommons.org/licenses/by-sa/4.0/)
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