Help with small program

[Felix Benner]

smartbei schrieb:
> Hello, I am a newbie with python, though I am having a lot of fun using
> it. Here is one of the excersizes I am trying to complete:
> the program is supposed to find the coin combination so that with 10
> coins you can reach a certain amoung, taken as a parameter. Here is the
> current program:
> 
> coins = (100,10,5,1,0.5)
> anslist = []
> def bar(fin, hist = {100:0,10:0,5:0,1:0,0.5:0}):
> 	s = sum(x*hist[x] for x in hist)
> 	l = sum(hist.values())
> 	if s < fin and l < 10:
> 		for c in coins:
> 			if (s+c) <= fin:
> 				hist[c] += 1
> 				bar(fin, hist)
> 				hist[c] -= 1
> 	elif l==10 and s==fin and not hist in anslist:
> 		#p1
> 		anslist.append(hist)
> 
> bar(50)
> print anslist
> 
> The problem is that if I run it, anslist prints as [{0.5: 0, 1: 0, 10:
> 0, 100: 0, 5: 0}], which doesnt even add up to 50. When I check how
> many times the program has reached the #p1 by sticking a print there,
> it only reaches it once, and it comes out correct. why is it that this
> result is replaced by the incorrect final one?
> 

hist is stored in anslist as a pointer only, therfore the hist[c] -= 1
operates on the same dict as is stored in the anslist. Try the following
in the python interpreter:

a = { 'key' : 1 }
l = [a]
l[0]['key'] -= 1
a

instead use:

anslist.append(dict(hist.items))

which will copy the dict.