A brainfuck interpreter written in python

brainfuck.py

#!/usr/bin/env python3
import sys

"""
A brainfuck interpreter written in python

Example usage: python3 brainfck.py test.bfck

Contents of test.bfck:
---------------------
    ,[-.>+<];
"""

# allocate memory 
mem = [0]

# initialize data pointer
dp = 0

def last_index(l,what):
    n = (len(l) - i - 1 for i,v in enumerate(reversed(l)) if v == what)
    return next(n) 

def loop(commands,main=False):
    global mem
    global dp
     
    cp = 0
    dp0 = dp
    
    while True:
        c = commands[cp]
       
        if c == '>':
            dp += 1
            try:
                mem[dp]
            except IndexError:
                mem += [0]
        elif c == '<':
            dp -= 1  
        elif c == '+':
            mem[dp] += 1
        elif c == '-':
            mem[dp] -= 1
        elif c == '.':
            print(mem[dp])
        elif c == ',':
            mem[dp] = int(input())
        elif c == '[':
            j = last_index(commands,']')
            loop(commands[cp+1:j+1])
            commands = commands[:cp+1] + commands[j+1:]
        
        # go back to start of the loop
        if c == ']':
            if not mem[dp0] and not main:
                break
            else:
                cp = 0 
        elif c == ';' and main:
            break
        else:
            cp += 1

# read the specified program file
with open(sys.argv[1]) as f:
    program = list(''.join(f.read().split()))

loop(program,True)