Brainfuck interpreter that isn't complete garbage and does not abuse OOP like every other version I found online

brainfuck.py

#flags - 2012
#wtfplv2
import sys

if not len(sys.argv)==2:
	print 'Usage: brainfuck.py <file>'
	sys.exit(1)

PROGRAM = bytearray(9999)
CELL = 0
LOOPS = []
LOOP = -1
INDEX = 0

def compile(instructions):
	global PROGRAM,CELL,LOOPS,LOOP,INDEX
	_buffer = ''
	
	END_INDEX = len(instructions)
	
	while INDEX<=END_INDEX:
		if INDEX == END_INDEX:
			
			if INDEX >= len(instructions):
				break
			
			END_INDEX = len(instructions)
		
		char = instructions[INDEX]
		
		if char=='+':
			PROGRAM[CELL]+=1
		elif char=='-':
			PROGRAM[CELL]-=1
		elif char=='>':
			CELL+=1
		elif char=='<':
			CELL-=1
		elif char=='.':
			_buffer+=str(chr(PROGRAM[CELL]))
		elif char==',':
			print '# ',
			PROGRAM[CELL] = ord(raw_input())
		elif char=='[':
			LOOP+=1
			LOOPS.append({'start':INDEX,'end':-1})
		elif char==']':
			if LOOP>-1:
				_loop = ''
				LOOPS[LOOP]['end'] = INDEX
				
				if PROGRAM[CELL]:
					INDEX = LOOPS[LOOP]['start']-1
					END_INDEX = LOOPS[LOOP]['end']
				
				LOOPS.pop(LOOP)
				LOOP-=1
			else:
				raise Exception('Brace mismatch. No open loops.')
		
		INDEX+=1
	
	return _buffer

with open(sys.argv[1],'r') as _source:
	_instructions = ''
	for line in _source.readlines():		
		for char in line:
			if char in ['+','-','<','>','[',']','.',',']:
				_instructions+=char
	
	print compile(_instructions),