Execute Brain****/Python

From Rosetta Code
Execute Brain****/Python is an implementation of Brainf***. Other implementations of Brainf***.
Execute Brain****/Python is part of RCBF. You may find other members of RCBF at Category:RCBF.

Implementation of a Brainfuck interpreter in Python.

#!/usr/bin/python
import sys
import collections
#from collections import defaultdict instead since this only uses defaultdict?
 
def brainfuck (fd=None):
fd = fd or (open(sys.argv[1]) if sys.argv[1:] else sys.stdin)
source = fd.read()
loop_ptrs = {}
loop_stack = []
for ptr, opcode in enumerate(source):
if opcode == '[': loop_stack.append(ptr)
if opcode == ']':
if not loop_stack:
source = source[:ptr]
break
sptr = loop_stack.pop()
loop_ptrs[ptr], loop_ptrs[sptr] = sptr, ptr
if loop_stack:
raise SyntaxError ("unclosed loops at {}".format(loop_stack))
tape = collections.defaultdict(int)
cell = 0
ptr = 0
while ptr < len(source):
opcode = source[ptr]
if opcode == '>': cell += 1
elif opcode == '<': cell -= 1
elif opcode == '+': tape[cell] += 1
elif opcode == '-': tape[cell] -= 1
elif opcode == ',': tape[cell] = ord(sys.stdin.read(1))
elif opcode == '.': sys.stdout.write(chr(tape[cell]))
elif (opcode == '[' and not tape[cell]) or \
(opcode == ']' and tape[cell]): ptr = loop_ptrs[ptr]
ptr += 1
 
if __name__ == "__main__": brainfuck()