BF formatter

# python 3
# bf_format - format brainfuck code listings using nested indentation
# updated 2019-05-26-09:23 comment out the lf insertion for ']'
#   I think it looks better this way, also results in shorter listing

ilv = -1
ich = "    " # indent character - four regular spaces
prog = ""    # store the whole program in a variable
command_set = "><+-,.[]"

f = open(input("bf file: "), 'r')
# read file
while True:
   nextch = f.read(1)
   if(not nextch):
       f.close()
       break
   if(nextch in command_set):
       prog += (nextch)
# format
for i in range(len(prog)):
    if(prog[i] == "["):
        print()
        ilv += 1
        print(ich * ilv, end = "")
    if(prog[i] == "]"):
#        print()                     # remove lf after ']'
#        print(ich * ilv, end = "")
        ilv -= 1
    print(prog[i], end = "")