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#!/usr/bin/python2
"""
A Brainf_ck interpreter in Python
Copyright (c) 2014 by Mark Wolstenholme
released under GPL v3 or later

I'll assume you know what Brainf_ck is:
> 	Increment the pointer.
< 	Decrement the pointer.
+ 	Increment the byte at the pointer.
- 	Decrement the byte at the pointer.
. 	Output the byte at the pointer.
, 	Input a byte and store it in the byte at the pointer.
&#91; 	Jump forward past the matching &#93; if the byte at the pointer is zero.
&#93; 	Jump backward to the matching &#91; unless the byte at the pointer is zero.
"""
from sys import argv

class Brainf_ck&#58;
    'Brainf_ck class.'

    def __init__&#40;self&#41;&#58;
        'Set up the internals'
        # give it 64k to play with
        self.storage = bytearray&#40;65536&#41; 
        # We also need somewhere to store the locations of the &#91; and &#93;
        self.loopstarts, self.loopends = &#123;&#125;, &#123;&#125;
        # build an output string internally
        self.output = ''
        # We need an input string
        self.inpt = ''
        # And we need a storage pointer and a program counter
        self.pointer, self.counter = 0, 0
        # Instructions dictionary mapped to functions of this class
        self.instructions = &#123;
            '>'&#58; self._inc,
            '<'&#58; self._dec,
            '+'&#58; self._p_inc,
            '-'&#58; self._p_dec,
            '.'&#58; self._to_out,
            ','&#58; self._from_in,
            '&#91;'&#58; self._forward,
            '&#93;'&#58; self._back
        &#125;

    def _inc&#40;self&#41;&#58;
        'Increment the pointer. >'
        self.pointer = &#40;self.pointer + 1&#41; % len&#40;self.storage&#41;

    def _dec&#40;self&#41;&#58;
        'Decrement the pointer. <'
        self.pointer = &#40;self.pointer - 1&#41; % len&#40;self.storage&#41;

    def _p_inc&#40;self&#41;&#58;
        'Increment the byte at the pointer. +'
        self.storage&#91;self.pointer&#93; = &#40;self.storage&#91;self.pointer&#93; + 1&#41; % 256

    def _p_dec&#40;self&#41;&#58;
        'Decrement the byte at the pointer. -'
        self.storage&#91;self.pointer&#93; = &#40;self.storage&#91;self.pointer&#93; - 1&#41; % 256

    def _to_out&#40;self&#41;&#58;
        'Output the byte at the pointer. .'
        self.output += chr&#40;self.storage&#91;self.pointer&#93;&#41;

    def _from_in&#40;self&#41;&#58;
        'Input a byte and store it in the byte at the pointer. ,'
        if self.inpt == ''&#58;
            self.storage&#91;self.pointer&#93; = 255 # -1 as EOF
        else&#58;
            self.storage&#91;self.pointer&#93; = ord&#40;self.inpt&#91;0&#93;&#41;
            self.inpt = self.inpt&#91;1&#58;&#93;

    def _forward&#40;self&#41;&#58;
        'Jump forward past the matching &#93; if the byte at the pointer is zero. &#91;'
        if self.storage&#91;self.pointer&#93; == 0&#58;
            self.counter = self.loopends&#91;self.counter&#93;

    def _back&#40;self&#41;&#58;
        'Jump backward to the matching &#91; unless the byte at the pointer is zero. &#93;'
        if self.storage&#91;self.pointer&#93; != 0&#58;
            self.counter = self.loopstarts&#91;self.counter&#93;

    def document&#40;self&#41;&#58;
        'Output some documentation.'
        self.output = 'A Brainf_ck interpreter in Python\n'
        self.output += '\n'
        self.output += 'Usage&#58;\n'
        self.output += 'brainf_ck.py <BRAINF_CKCODE> &#91;<INPUTSTRING>&#93;'

    def interpret&#40;self, bfcode, inpt&#41;&#58;
        'Run the bfcode using inputstring inpt.'
        self._find_loops&#40;bfcode&#41;
        self.inpt = inpt
        while self.counter < len&#40;bfcode&#41;&#58;
            if bfcode&#91;self.counter&#93; in self.instructions&#58;
                self.instructions&#91;bfcode&#91;self.counter&#93;&#93;&#40;&#41;
            self.counter += 1

    def _find_loops&#40;self, bfcode&#41;&#58;
        'Store the locations of &#91; and &#93; for looping'
        stack = &#91;&#93;
        for a in range&#40;len&#40;bfcode&#41;&#41;&#58;
            if bfcode&#91;a&#93; == '&#91;'&#58;
                stack.append&#40;a&#41;
            if bfcode&#91;a&#93; == '&#93;'&#58;
                self.loopstarts&#91;a&#93; = stack&#91;-1&#93;
                self.loopends&#91;stack&#91;-1&#93;&#93; = a
                stack = stack&#91;&#58;-1&#93;
        if len&#40;stack&#41; != 0&#58;
            raise SyntaxError&#40;'Mismatching &#91;&#93;'&#41;

if __name__ == "__main__"&#58;
    bf = Brainf_ck&#40;&#41;
    if len&#40;argv&#41; == 1&#58;
        bf.document&#40;&#41;
    elif len&#40;argv&#41; == 2&#58;
        bf.interpret&#40;argv&#91;1&#93;, ''&#41;
    else&#58;
        bf.interpret&#40;argv&#91;1&#93;, argv&#91;2&#93;&#41;
    print bf.output