Python Tkinter Canvas Rectangle Selection Box

"""Rect Tracker class for Python Tkinter Canvas"""

def groups(glist, numPerGroup=2):
	result = []

	i = 0
	cur = []
	for item in glist:
		if not i < numPerGroup:
			result.append(cur)
			cur = []
			i = 0

		cur.append(item)
		i += 1

	if cur:
		result.append(cur)

	return result

def average(points):
	aver = [0,0]
	
	for point in points:
		aver[0] += point[0]
		aver[1] += point[1]
		
	return aver[0]/len(points), aver[1]/len(points)

class RectTracker:
	
	def __init__(self, canvas):
		self.canvas = canvas
		self.item = None
		
	def draw(self, start, end, **opts):
		"""Draw the rectangle"""
		return self.canvas.create_rectangle(*(list(start)+list(end)), **opts)
		
	def autodraw(self, **opts):
		"""Setup automatic drawing; supports command option"""
		self.start = None
		self.canvas.bind("<Button-1>", self.__update, '+')
		self.canvas.bind("<B1-Motion>", self.__update, '+')
		self.canvas.bind("<ButtonRelease-1>", self.__stop, '+')
		
		self._command = opts.pop('command', lambda *args: None)
		self.rectopts = opts
		
	def __update(self, event):
		if not self.start:
			self.start = [event.x, event.y]
			return
		
		if self.item is not None:
			self.canvas.delete(self.item)
		self.item = self.draw(self.start, (event.x, event.y), **self.rectopts)
		self._command(self.start, (event.x, event.y))
		
	def __stop(self, event):
		self.start = None
		self.canvas.delete(self.item)
		self.item = None
		
	def hit_test(self, start, end, tags=None, ignoretags=None, ignore=[]):
		"""
		Check to see if there are items between the start and end
		"""
		ignore = set(ignore)
		ignore.update([self.item])
		
		# first filter all of the items in the canvas
		if isinstance(tags, str):
			tags = [tags]
		
		if tags:
			tocheck = []
			for tag in tags:
				tocheck.extend(self.canvas.find_withtag(tag))
		else:
			tocheck = self.canvas.find_all()
		tocheck = [x for x in tocheck if x != self.item]
		if ignoretags:
			if not hasattr(ignoretags, '__iter__'):
				ignoretags = [ignoretags]
			tocheck = [x for x in tocheck if x not in self.canvas.find_withtag(it) for it in ignoretags]
		
		self.items = tocheck
		
		# then figure out the box
		xlow = min(start[0], end[0])
		xhigh = max(start[0], end[0])
		
		ylow = min(start[1], end[1])
		yhigh = max(start[1], end[1])
		
		items = []
		for item in tocheck:
			if item not in ignore:
				x, y = average(groups(self.canvas.coords(item)))
				if (xlow < x < xhigh) and (ylow < y < yhigh):
					items.append(item)
	
		return items

def main():
	from random import shuffle
	
	canv = Canvas(width=500, height=500)
	canv.create_rectangle(50, 50, 250, 150, fill='red')
	canv.pack(fill=BOTH, expand=YES)
	
	rect = RectTracker(canv)
	# draw some base rectangles
	rect.draw([50,50], [250, 150], fill='red', tags=('red', 'box'))
	rect.draw([300,300], [400, 450], fill='green', tags=('gre', 'box'))
	
	# just for fun
	x, y = None, None
	def cool_design(event):
		global x, y
		kill_xy()
		
		dashes = [3, 2]
		x = canv.create_line(event.x, 0, event.x, 1000, dash=dashes, tags='no')
		y = canv.create_line(0, event.y, 1000, event.y, dash=dashes, tags='no')
		
	def kill_xy(event=None):
		canv.delete('no')
	
	canv.bind('<Motion>', cool_design, '+')
	
	# command
	def onDrag(start, end):
		global x,y
		items = rect.hit_test(start, end)
		for x in rect.items:
			if x not in items:
				canv.itemconfig(x, fill='grey')
			else:
				canv.itemconfig(x, fill='blue')
	
	rect.autodraw(fill="", width=2, command=onDrag)
	
	mainloop()

if __name__ == '__main__':
	try:
		from tkinter import *
	except ImportError:
		from Tkinter import *
	main()