BF interpreter

gistfile1.py

import sys

#read Brainfuck from file and filter
filename = sys.argv[1]

with open(filename) as f:
	bf = f.read()

legal = set('><+-.,[]')
bf = ''.join(c for c in bf if c in legal)
print(bf)

#set index (current cell), array (memory), and ipointer(command pointer)
index = 0
array = [0] * 100
ipointer = 0

def right():
	global index
	global ipointer
	index += 1
	ipointer += 1

def left():
	global index
	global ipointer
	index -= 1
	ipointer += 1

def increment():
	global array
	global index
	global ipointer
	array[index] += 1
	ipointer += 1

def decrement():
	global array
	global index
	global ipointer
	if array[index] == 0:
		array[index] = 255
	else:
		array[index] -= 1
	ipointer += 1

def output():
	global array
	global index
	global ipointer
	sys.stdout.write(chr(array[index]))
	ipointer += 1

def accept():
	global array
	global index
	global ipointer
	inv = ord(sys.stdin.read(1))
	print(inv)
	array[index] = inv
	ipointer += 1

def openloop():
	global array
	global index
	global ipointer
	global bf

	if array[index] == 0:
		nest = 1
		while nest != 0:
			ipointer += 1
			if bf[ipointer] == "]":
				nest -= 1
			elif bf[ipointer] == "[":
				nest += 1
		ipointer += 1
	else:
		ipointer += 1

def closeloop():
	global array
	global index
	global ipointer
	global bf
	
	if array[index] != 0:
		nest = 1
		while nest != 0:
			ipointer -= 1
			if bf[ipointer] == "[":
				nest -= 1
			elif bf[ipointer] == "]":
				nest += 1
	else:
		ipointer += 1

commandmap = {'<':left, 
				'>':right, 
				'+':increment, 
				'-':decrement,
				'.':output,
				',':accept,
				'[':openloop,
				']':closeloop
				}

counter = 0
while ipointer < len(bf) and counter < 1000:
	commandmap[bf[ipointer]]()
	counter += 1