Added solution code

Solutions/4_4/fileparse.py

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+# fileparse.py
+import csv
+
+def parse_csv(lines, select=None, types=None, has_headers=True, delimiter=',', silence_errors=False):
+    '''
+    Parse a CSV file into a list of records with type conversion.
+    '''
+    if select and not has_headers:
+        raise RuntimeError('select requires column headers')
+
+    rows = csv.reader(lines, delimiter=delimiter)
+
+    # Read the file headers (if any)
+    headers = next(rows) if has_headers else []
+
+    # If specific columns have been selected, make indices for filtering and set output columns
+    if select:
+        indices = [ headers.index(colname) for colname in select ]
+        headers = select
+
+    records = []
+    for rowno, row in enumerate(rows, 1):
+        if not row:     # Skip rows with no data
+            continue
+
+        # If specific column indices are selected, pick them out
+        if select:
+            row = [ row[index] for index in indices]
+
+        # Apply type conversion to the row
+        if types:
+            try:
+                row = [func(val) for func, val in zip(types, row)]
+            except ValueError as e:
+                if not silence_errors:
+                    print(f"Row {rowno}: Couldn't convert {row}")
+                    print(f"Row {rowno}: Reason {e}")
+                continue
+
+        # Make a dictionary or a tuple
+        if headers:
+            record = dict(zip(headers, row))
+        else:
+            record = tuple(row)
+        records.append(record)
+
+    return records

Solutions/4_4/pcost.py

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+# pcost.py
+
+import report
+
+def portfolio_cost(filename):
+    '''
+    Computes the total cost (shares*price) of a portfolio file
+    '''
+    portfolio = report.read_portfolio(filename)
+    return sum([s.cost() for s in portfolio])
+
+def main(args):
+    if len(args) != 2:
+        raise SystemExit('Usage: %s portfoliofile' % args[0])
+    filename = args[1]
+    print('Total cost:', portfolio_cost(filename))
+
+if __name__ == '__main__':
+    import sys
+    main(sys.argv)

Solutions/4_4/report.py

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+# report.py
+
+import fileparse
+from stock import Stock
+
+def read_portfolio(filename):
+    '''
+    Read a stock portfolio file into a list of dictionaries with keys
+    name, shares, and price.
+    '''
+    with open(filename) as lines:
+        portdicts = fileparse.parse_csv(lines, 
+                                        select=['name','shares','price'], 
+                                        types=[str,int,float])
+
+    portfolio = [ Stock(d['name'], d['shares'], d['price']) for d in portdicts ]
+    return portfolio
+
+def read_prices(filename):
+    '''
+    Read a CSV file of price data into a dict mapping names to prices.
+    '''
+    with open(filename) as lines:
+        return dict(fileparse.parse_csv(lines, types=[str,float], has_headers=False))
+
+def make_report_data(portfolio, prices):
+    '''
+    Make a list of (name, shares, price, change) tuples given a portfolio list
+    and prices dictionary.
+    '''
+    rows = []
+    for s in portfolio:
+        current_price = prices[s.name]
+        change = current_price - s.price
+        summary = (s.name, s.shares, current_price, change)
+        rows.append(summary)
+    return rows
+
+def print_report(reportdata):
+    '''
+    Print a nicely formated table from a list of (name, shares, price, change) tuples.
+    '''
+    headers = ('Name','Shares','Price','Change')
+    print('%10s %10s %10s %10s' % headers)
+    print(('-'*10 + ' ')*len(headers))
+    for row in reportdata:
+        print('%10s %10d %10.2f %10.2f' % row)
+
+def portfolio_report(portfoliofile, pricefile):        
+    '''
+    Make a stock report given portfolio and price data files.
+    '''
+    # Read data files 
+    portfolio = read_portfolio(portfoliofile)
+    prices = read_prices(pricefile)
+
+    # Create the report data
+    report = make_report_data(portfolio, prices)
+
+    # Print it out
+    print_report(report)
+
+def main(args):
+    if len(args) != 3:
+        raise SystemExit('Usage: %s portfile pricefile' % args[0])
+    portfolio_report(args[1], args[2])
+
+if __name__ == '__main__':
+    import sys
+    main(sys.argv)

Solutions/4_4/stock.py

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+# stock.py
+
+class Stock(object):
+    '''
+    An instance of a stock holding consisting of name, shares, and price.
+    '''
+    def __init__(self, name, shares, price):
+        self.name   = name
+        self.shares = shares
+        self.price  = price
+
+    def cost(self):
+        '''
+        Return the cost as shares*price
+        '''
+        return self.shares * self.price
+
+    def sell(self, nshares):
+        '''
+        Sell a number of shares
+        '''
+        self.shares -= nshares
+