Format brainfuck code listings using nested indentation

bf_format.py

#!/usr/bin/env python3
# bf_format - format brainfuck code listings using nested indentation
# originally from https://pastebin.com/raw/FN1YMQ6r
# updated 2019-05-26-09:23 comment out the lf insertion for ']'
#   I think it looks better this way, also results in shorter listing
# updated 2022-06-11 convert to use argv, add '-i' arg

from io import StringIO
from pathlib import Path
from sys import argv, stdout

if not argv[1:]:
  argv.append("-")

inplace = False
for arg in argv[1:]:
  if arg == "-i":
    inplace = True
    continue
  if arg == "-":
    file = open(0, "rb")
  else:
    file = Path(arg).open("rb")
  with file:
    text = file.read()
  
  output = stdout
  if inplace:
    output = Path(arg).open("w", encoding="utf-8")
  
  with StringIO(text.decode("utf-8")) as f:
    ilv = -1
    ich = "    " # indent character - four regular spaces
    prog = ""    # store the whole program in a variable
    command_set = "><+-,.[]"
    # 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(file=output)
            ilv += 1
            print(ich * ilv, end = "", file=output)
        if(prog[i] == "]"):
    #        print()                     # remove lf after ']'
    #        print(ich * ilv, end = "")
            ilv -= 1
        print(prog[i], end = "", file=output)
        
  if inplace:
    output.close()
    inplace = False