At 07:31 AM 8/6/2007, Dick Moores wrote: >At 06:49 AM 8/6/2007, Kent Johnson wrote: > >Dick Moores wrote: > >>http://www.rcblue.com/Python/changeMaker_revised_for_US_denominations.py > >>I'm still working at Python--been at it a while--and thought the > >>script was ingenious. Do the Tutors agree? Or is it just > >>run-of-the-mill programming? Could it have been more simply written? > > > >I don't find it either ingenious or well-written. The algorithm is > >the same one you would use to count out an amount by hand so it > >doesn't seem so unusual. IMO the code relies too much on indices. If > >you rewrite it using a dict (or, even better, defaultdict(int)) for > >coinCount, there is no need for indices at all. Even with coinCount > >as a list, it could be better written. > > > >coinCount = [] > >for d in denominations: > > coinCount.append(0) > > > >=> > > > >coinCount = [0] * ndenominations > > > > > >The main loop could be > >for deno in range(ndenominations): > > if not remaining: > > break > > > >or > >for i, deno in enumerate(denominations): > ># i is now the index, deno is the actual denomination > > > > > >but I would write it this way and avoid the use of the index completely: > > > >from collections import defaultdict > >coinCount = defaultdict(int) > >remaining = change > > > ># Loop until either we have given all the change or we have > ># run out of coin denominations to check. > >for deno in denominations: > > if not remaining: > > break > > > > # For one denomination, count out coins of that denomination > > # as long as the remaining amount is greater than the denomination > > # amount. > > > > while remaining >= deno: > > coinCount[deno] += 1 > > print "remaining =", remaining > > remaining -= deno > > > ># Report the results. > >print "Your change is $%.02f"% (float(change) / CPD) > >for deno in denominations: > > if coinCount[deno] > 0: > > if deno >= 100: > > print "$%d bills:\t" % (deno / CPD), coinCount[deno] > > else: > > print "%d-cent coins:\t" % (deno), coinCount[deno] > > > > > >Kent > >Thanks Kent! > >Here's what I have after incorporating your suggestions: > >================================= >#!/usr/bin/env python >#coding=utf-8 >from collections import defaultdict > >CPD = 100 >cost = int(CPD * float(raw_input("Enter the cost: "))) >tend = int(CPD * float(raw_input("Enter the tendered amount: "))) > ># Calculate the change. >change = tend - cost > >coinCount = defaultdict(int) >print coinCount >remaining = change >denominations = (2000, 1000, 500, 100, 50, 25, 10, 5, 1) > ># Loop until either we have given all the change or we have ># run out of coin denominations to check. >for deno in denominations: > if not remaining: > break > > > # For one denomination, count out coins of that denomination > # as long as the remaining amount is greater than the denomination > # amount. > > > while remaining >= deno: > coinCount[deno] += 1 > remaining -= deno > > ># Report the results. >print "Your change is $%.02f"% (float(change) / CPD) >for deno in denominations: > if coinCount[deno] > 0: > if deno >= 100: > print "$%d bills:\t" % (deno / CPD), coinCount[deno] > else: > print "%d-cent coins:\t" % (deno), coinCount[deno] >======================================== > >Gotta say though, I still don't understand how the defaultdict works here. > >Dick
I was just about finished with a script that would tell the clerk how to give the change to the customer, when I discovered that the above script computes the wrong amount of change in certain situations. It works fine if the customer tenders only bills and no change, but that's not realistic. For example, if the cost is $1.78 the customer may well tender $2.03 so he can get a quarter back rather than 2 dimes and 2 pennies. But the script in that case will compute change of 24 cents! Try it out. I've put the same script on the web, but deleted the line that I'd left in by mistake, "print coinCount". So, does this mean I should use the decimal module? Or is there another way to fix the problem? Thanks, Dick _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
