stocks.py

from decimal import Decimal
from csv import DictReader, DictWriter
from datetime import datetime, timedelta
from urllib import urlopen, urlencode
import sys
from pprint import pprint
from itertools import chain

URL = 'http://ichart.yahoo.com/table.csv'

def map_price(symbol, price):
    return { 'symbol'         : symbol, 
             'date'           : datetime.strptime(price['Date'], '%Y-%m-%d'),
             'open'           : Decimal(price['Open']), 
             'close'          : Decimal(price['Close']), 
             'adjusted_close' : Decimal(price['Adj Close']), 
             'high'           : Decimal(price['High']), 
             'low'            : Decimal(price['Low']), 
             'volume'         : int(price['Volume']) }  

def historical(symbol, start_date, end_date):

    params = { 's'      : symbol, 
               'd'      : '%02d' % end_date.day,
               'e'      : '%02d' % end_date.month,
               'f'      : str(end_date.year),
               'g'      : 'd', 
               'a'      : '%02d' % start_date.day,
               'b'      : '%02d' % start_date.month,
               'c'      : str(start_date.year), 
               'ignore' : '.csv' }

    url = URL + '?' + urlencode(params)

    return ( map_price(symbol, i) for i in DictReader(urlopen(url)) )

if __name__ == '__main__':

    end   = datetime.now()
    start = end + timedelta(days=-365)
    
    symbols = (i.upper() for i in sys.argv[1:])
    prices  = chain( *(historical(symbol, start, end) for symbol in symbols ))

    fields = ('symbol', 'date', 'open', 'close', 'adjusted_close', 'high', 'low', 'volume')
    writer = DictWriter(sys.stdout, fields)
    writer.writerow(dict( (i,i) for i in fields))
    writer.writerows(prices)