def init_goban(size=9):
	"""
	Returns an empty goban in the form of a dictionary where the keys are 
	x,y-tuples: (1,1) is the upper left corner, (9,9) the lower right one 
	for a 9x9 goban.
	The additional key named size contains the length of a side of the goban.
	Content of a field:
	0 == empty field
	1 == white stone on field
	2 == black stone on field
	Field turn_number: Current turn to be played. Even: white, uneven: black.
	Optional argument size: define length of a side of the goban (one of
	9, 12 or 19). Defaults to 9.
	Returns dictionary.
	"""
	goban = {}
	for x in range(1,size+1):
		for y in range(1,size+1):
			goban[(x,y)] = 0
	if (size == 9) or (size == 13) or (size == 19):
		goban["size"] = size
	else:
		goban["size"] = 9
	goban["turn_number"] = 1

	#some stones for testing purposes
	goban[(1,2)] = 1;	goban[(2,1)] = 1;	goban[(2,3)] = 1;	goban[(3,3)] = 1;	goban[(6,7)] = 1;	goban[(6,9)] = 1
	goban[(2,2)] = 2;	goban[(1,3)] = 2;	goban[(4,7)] = 2;	goban[(4,9)] = 2;	goban[(5,8)] = 2;	goban[(7,9)] = 2	

	return goban


def save_goban(goban):
	"""gets a goban dictionary and pickles it to a file.
	"""
	try:
		f = open(picklefile,"w")
		pickle.dump(goban,f)
		f.close()			
	except:
		print "error: could not write to file "+picklefile+"!"

def load_goban():	
	"""trys to load and return a pickled goban. If this does not work return
	a newly initialized goban."""
	try:
		f = open(picklefile,"r")		
		return pickle.load(f)
		f.close()			#datei ist jetzt genullt
	except:
		return init_goban()