Interactive complete Brainfuck Interpreter

Question

This is another Brainfuck interpreter in Python. I personaly think this is better than most of the other once you find online, because it keeps a bracket_map, which makes both [ and ] instant actions. The data array is a simple defaultdict(int), so it is infinite is size in both directions (which maybe a bad decision?) I am open to all critics and hope that somebody can tell if this is realy as efficient as I think.

from collections import defaultdict
from msvcrt import getch
program = "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."
def evaluate(sourcecode):
 bracket_map = {}
 stack = []
 for i, c in enumerate(sourcecode):
 if c == "[":
 stack.append(i)
 elif c == "]":
 s = stack.pop()
 bracket_map[s], bracket_map[i] = i, s
 assert not stack
 del stack
 data = defaultdict(int)
 data_index = 0
 program_index = 0
 while program_index < len(sourcecode):
 c = sourcecode[program_index]
 if c == "+":
 v = data[data_index] + 1
 if v > 255:
 v = 0
 data[data_index] = v
 elif c == "-":
 v = data[data_index] - 1
 if v < 0:
 v = 255
 data[data_index] = v
 elif c == ">":
 data_index += 1
 elif c == "<":
 data_index -= 1
 elif c == ".":
 print(chr(data[data_index]), end="")
 elif c == ",":
 data[data_index] = getch()[0]
 elif c == "[":
 if not data[data_index]:
 program_index = bracket_map[program_index]
 elif c == "]":
 if data[data_index]:
 program_index = bracket_map[program_index]
 program_index += 1
evaluate(program)

(if you are not on windows, you need an alternative for the getch function)

Answer 1

All in all this looks good to me. I would make 2 changes

bracket_map

The code to assemble this map can be more clear in it's own function.

+ and -

v = data[data_index] - 1
if v < 0:
 v = 255
data[data_index] = v

can be easily replaced by

data[data_index] = (data[data_index] - 1) % 256

Same goes for the + operation

• MegaIng: I always forget about module of negative numbers.