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Exercises/soln3_3.md

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+# Exercise 3.3 - Solution
+
+```python
+# stock.py
+
+class Stock:
+    types = (str, int, float)
+    def __init__(self, name, shares, price):
+        self.name = name
+        self.shares = shares
+        self.price = price
+
+    def cost(self):
+        return self.shares * self.price
+
+    def sell(self, nshares):
+        self.shares -= nshares
+
+    @classmethod
+    def from_row(cls, row):
+        values = [func(val) for func, val in zip(cls.types, row)]
+        return cls(*values)
+
+def read_portfolio(filename):
+    '''
+    Read a CSV file of stock data into a list of Stocks
+    '''
+    import csv
+    portfolio = []
+    with open(filename) as f:
+        rows = csv.reader(f)
+        headers = next(rows)
+        for row in rows:
+            record = Stock.from_row(row)
+            portfolio.append(record)
+    return portfolio
+
+if __name__ == '__main__':
+    import tableformat
+    import reader
+    portfolio = read_portfolio('Data/portfolio.csv')
+    
+    # Generalized version
+    # portfolio = reader.read_csv_as_instances('Data/portfolio.csv', Stock)
+    tableformat.print_table(portfolio, ['name', 'shares', 'price'])
+```
+
+The `reader.py` file should now look like this:
+
+```python
+# reader.py
+
+import csv
+from collections import defaultdict
+
+def read_csv_as_dicts(filename, types):
+    '''
+    Read a CSV file into a list of dicts with column type conversion
+    '''
+    records = []
+    with open(filename) as f:
+        rows = csv.reader(f)
+        headers = next(rows)
+        for row in rows:
+            record = { name: func(val) for name, func, val in zip(headers, types, row) }
+            records.append(record)
+    return records
+
+def read_csv_as_instances(filename, cls):
+    '''
+    Read a CSV file into a list of instances
+    '''
+    records = []
+    with open(filename) as f:
+        rows = csv.reader(f)
+        headers = next(rows)
+        for row in rows:
+            records.append(cls.from_row(row))
+    return records
+```
+
+
+
+[Back](ex3_3.md)