python-mastery/Exercises/ex3_1.md

\[ [Index](index.md) | [Exercise 2.6](ex2_6.md) | [Exercise 3.2](ex3_2.md) \]

# Exercise 3.1

*Objectives:*

- Define a simple class

*Files Modified:* `stock.py`

In [Exercise 1.5](ex1_5.md), you defined a simple class
`Stock` for representing a holding of stock.  In this exercise,
we're simply going to add a few features to that class as well as
write some utility functions.

## (a) Adding a new method

Add a new method `sell(nshares)` to Stock that sells a certain number
of shares by decrementing the share count.  Have it work like this:

```python
>>> s = Stock('GOOG',100,490.10)
>>> s.shares
100
>>> s.sell(25)
>>> s.shares
75
>>>
```

## (b) Reading a portfolio

Add a function `read_portfolio()` to your `stock.py` program that
reads a file of portfolio data into a list of `Stock` objects. Here's how it should work:

```python
>>> portfolio = read_portfolio('Data/portfolio.csv')
>>> for s in portfolio:
        print(s)

<__main__.Stock object at 0x3902f0>
<__main__.Stock object at 0x390270>
<__main__.Stock object at 0x390330>
<__main__.Stock object at 0x390370>
<__main__.Stock object at 0x3903b0>
<__main__.Stock object at 0x3903f0>
<__main__.Stock object at 0x390430>
>>>
```

You already wrote a similar function as part of
[Exercise 2.3](ex2_3.md).  Design discussion: Should
`read_portfolio()` be a separate function or part of the class
definition?

## (c) Printing a Table

Table the data read in part (b) and use it to make a nicely formatted
table. For example:

```python
>>> portfolio = read_portfolio('Data/portfolio.csv')
>>> for s in portfolio:
           print('%10s %10d %10.2f' % (s.name, s.shares, s.price))

        AA        100      32.20
       IBM         50      91.10
       CAT        150      83.44
      MSFT        200      51.23
        GE         95      40.37
      MSFT         50      65.10
       IBM        100      70.44
>>>
```

Take this code and put it in a function `print_portfolio()` that 
produces the same output, but additionally adds some table headers.
For example:

```python
>>> portfolio = read_portfolio('Data/portfolio.csv')
>>> print_portfolio(portfolio)
      name     shares      price
---------- ---------- ---------- 
        AA        100      32.20
       IBM         50      91.10
       CAT        150      83.44
      MSFT        200      51.23
        GE         95      40.37
      MSFT         50      65.10
       IBM        100      70.44
>>>
```

\[ [Solution](soln3_1.md) | [Index](index.md) | [Exercise 2.6](ex2_6.md) | [Exercise 3.2](ex3_2.md) \]

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