<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def ticker(rest):
	"Look up a ticker symbol's current trading value"
	ticker = rest.upper()
	# let's use Yahoo's nifty csv facility, and pull last time/price both
	symbol = 's'
	last_trade_price = 'l1'
	last_trade_time = 't1'
	change_percent = 'p2'
	format = ''.join((symbol, last_trade_time, last_trade_price, change_percent))
	url = (
		'http://finance.yahoo.com/d/quotes.csv?s=%(ticker)s&f=%(format)s'
		% locals())
	stock_info = csv.reader(util.open_url(url).text.splitlines())
	last_trade, = stock_info
	ticker_given, time, price, diff = last_trade
	if ticker_given != ticker:
		return "d'oh... could not find information for symbol %s" % ticker
	return '%(ticker)s at %(time)s (ET): %(price)s (%(diff)s)' % locals()