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Brainfuck interpreter in a single line of Python
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README.md add README Aug 6, 2019
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README.md

Brainfuck interpreter in one line

According to this comment on reddit, it's possible to write every Python program (that doesn't throw exceptions) in just one line without using any semicolons.

Here's a photo of me shortly after reading that comment:

So I wrote a Brainfuck interpreter in just one line, with no semicolons. Tested with hello-world and rot13 in brainfuck. Use like this: python3 b.py some_bf_code.bf

Here's the thing in a more "readable" format:

with type("Com", (), {  # create a new type Com
    # define __enter__ and __exit__ methods to make the type available for
    # the with .. as .. syntax
    "__enter__": lambda  s: s,
    "__exit__":lambda s,e,v,t: 1,
    # import some modules and save them as class members
    "sys": __import__("sys"),
    "re": __import__("re"),
    "it": __import__("itertools"),
    "__init__": lambda s: [
        None,
        # initialize memory tape
        setattr(s, "mem", [0 for i in range(30000)]),
        # initialize pointer
        setattr(s, "ptr", 0),
        # initialize index (where are we in the code)
        setattr(s, "i", -1)
        # return the 0th element of this list (None), since __init__ must return None
        ][0],
    # this is the method that does all the work, it takes the code as input
    "do": lambda com,code: [ # first, create a list (to loop over code, see below)
        # this lambda gets called on every step
        # first, increase the index by 1
        (lambda: setattr(com, "i" ,com.i+1) or\
            # if the current symbol is '>' or '<', change the pointer accordingly
            (setattr(com, "ptr", com.ptr+1) if code[com.i]==">"\
            else setattr(com, "ptr", com.ptr-1) if code[com.i]=="<"\
            # if the current symbol is '+' or '-', change the memory at the pointer accordingly
            else com.mem.__setitem__(com.ptr, com.mem[com.ptr]+1) if code[com.i]=="+"\
            else com.mem.__setitem__(com.ptr, com.mem[com.ptr]-1) if code[com.i]=="-"\
            # input and output, using sys module
            else com.sys.stdout.write(chr(com.mem[com.ptr])) if code[com.i]=="."\
            else com.mem.__setitem__(com.ptr,ord(com.sys.stdin.read(1))) if code[com.i]==","\
            # move index forward to matching ]
            else setattr(com, "i", com.i +
                # here comes my fancy matching bracket finder
                (lambda string: [i for i in zip([m.start() for m in com.re.finditer('\[',string)][1:]+[len(string)],
                                                [m.start() for m in com.re.finditer(']',string)])\
                    if i[0]>i[1]][0][1])\
                # call the fancy matching bracket finder with the rest of the code if the
                # current symbol is '[' and the pointer points to a 0
                (code[com.i:])) if code[com.i]=="[" and com.mem[com.ptr]==0\
            # move index back to matching [
            else setattr(com, "i", len(code[:(com.i+1)]) -
                # fancy matching bracket finder pt. 2
                (lambda string:[i for i in zip([m.start() for m in com.re.finditer(']',string)][1:]+[len(string)],
                                               [m.start() for m in com.re.finditer('\[',string)])\
                    if i[0]>i[1]][0][1])\
                # call the fancy matching bracket finder with the code until here if the
                # current symbol is ']' and the pointer doesn't point to a 0
                (code[:(com.i+1)][::-1])-2) if code[com.i]=="]" and not com.mem[com.ptr]==0\
            else 1) # dummy else
        # call the outer lambda if there's still code left
        )() if com.i+1<len(code)\
        # exit otherwise
        else com.sys.exit()\
        # endless for loop, imitating a while loop
        for _ in com.it.repeat(0)]
# call the newly created type to make an instance
})()\
# assign that instance to com
as com:\
# call the do method with the code
com.do("".join(
    # only care about the relevant characters
    filter(lambda x:x in "+-[]><.,",
           # open the file that was given as an argument on the command line
           list(open(com.sys.argv[1]).read()))
))
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