Python BF Interpreter

import sys

cachesize = 100

cache = [0] * cachesize
pointer = 0
codeindex = 0
loopindex = 0

loop = False

if len(sys.argv) < 2:
    exit()

try:
    f = open(sys.argv[1], 'r')
except IOError:
    print "File not found, aborting."
    raw_input()
    exit()

code = f.read()

cache[0] = 0

codelength = len(code)

while codeindex < codelength:

    char = code[codeindex]

    if char == '>':
        pointer += 1
        if pointer > cachesize:
            print "Error: attempted to exceed cache size"
            raw_input()
            exit()
    elif char == '<':
        pointer -= 1
        if pointer < 0:
            print "Error: attempted to go below index 0"
            raw_input()
            exit()
    elif char == '.':
        sys.stdout.write(str(chr(cache[pointer])))
    elif char == '+':
        cache[pointer] += 1
        if cache[pointer] > 255:
            print "Error: attempted to exceed byte value"
            raw_input()
            exit()
    elif char == '-':
        cache[pointer] -= 1
        if cache[pointer] < 0:
            print "Error: attempted to generate negative value"
            raw_input()
            exit()
    elif char == ',':
        cache[pointer] = ord(raw_input("Input: ")[0])
    elif char == '[':
        loop = True
        loopindex = codeindex
    elif char == ']':
        if not loop:
            print "Error: ended non-existant loop"
            raw_input()
            exit()
        elif cache[pointer] != 0:
            codeindex = loopindex
            continue

    codeindex += 1

f.close()
raw_input()