使用python编写虚拟机解释器

港控/mmm° 2022-06-08 08:42 159阅读 0赞

本文参考自：[http://www.ituring.com.cn/article/199660][http_www.ituring.com.cn_article_199660]

虚拟机是用来解释字节码指令的，通过使用python构造一个虚拟机解释器可以学到很多关于程序语言的知识，下面是具体的代码：

#!/usr/bin/python3
    # encoding: utf-8
    
    from io import StringIO
    from collections import deque
    import tokenize
    import sys
    
    
    class Stack(deque):
        push = deque.append
    
        def top(self):
            return self[-1]
    
    
    class Machine:
        def __init__(self, code):
            self.data_stack = Stack()
            self.return_addr_stack = Stack()
            self.instruction_pointer = 0
            self.code = code
    
        def pop(self):
            return self.data_stack.pop()
    
        def push(self, value):
            self.data_stack.push(value)
    
        def top(self):
            return self.data_stack.top()
    
        def run(self):
            while self.instruction_pointer < len(self.code):
                opcode = self.code[self.instruction_pointer]
                self.instruction_pointer += 1
                self.dispatch(opcode)
    
        def dispatch(self, op):
            dispatch_map = {
                "%": self.mod,
                "*": self.mul,
                "+": self.plus,
                "-": self.minus,
                "/": self.div,
                "==": self.eq,
                "cast_int": self.cast_int,
                "cast_str": self.cast_str,
                "drop": self.drop,
                "dup": self.dup,
                "if": self.if_stmt,
                "jmp": self.jmp,
                "over": self.over,
                "print": self.print,
                "println": self.println,
                "read": self.read,
                "dump": self.dump,
                "stack": self.stack,
                "swap": self.swap,
            }
            if op in dispatch_map:
                dispatch_map[op]()
            elif isinstance(op, int):
                self.push(op)
            elif isinstance(op, str) and op[0] == op[-1] == '"':
                self.push(op[1:-1])
            else:
                raise RuntimeError("Unknown opcode: '%s'" % op)
    
        def mod(self):
            self.push(self.pop() % self.pop())
    
        def mul(self):
            self.push(self.pop() * self.pop())
    
        def plus(self):
            self.push(self.pop() + self.pop())
    
        def minus(self):
            self.push(self.pop() - self.pop())
    
        def div(self):
            self.push(self.pop() / self.pop())
    
        def eq(self):
            self.push(self.top() == self.top())
    
        def cast_int(self):
            self.push(int(self.pop()))
    
        def cast_str(self):
            self.push(str(self.pop()))
    
        def drop(self):
            self.pop()
    
        def dup(self):
            self.push(self.top())
    
        def if_stmt(self):
            false_clause = self.pop()
            true_clause = self.pop()
            test = self.pop()
            self.push(true_clause if test else false_clause)
    
        def jmp(self):
            addr = self.pop()
            if (isinstance(addr, int) and 0 <= addr < len(self.code)):
                self.instruction_pointer = addr
            else:
                raise RuntimeError("JMP address must be a valid integer.")
    
        def over(self):
            b = self.pop()
            a = self.pop()
            self.push(a)
            self.push(b)
            self.push(a)
    
        def print(self):
            sys.stdout.write(str(self.pop()))
            sys.stdout.flush()
    
        def println(self):
            sys.stdout.write("%s\n" % self.pop())
            sys.stdout.flush()
    
        def dump(self):
            pass
    
        def read(self):
            self.push(input())
    
        def stack(self):
            pass
    
        def swap(self):
            a = self.pop()
            b = self.pop()
            self.push(a)
            self.push(b)
    
    
    def parse(text):
        tokens = tokenize.generate_tokens(StringIO(text).readline)
        for toknum, tokval, _, _, _ in tokens:
            if toknum == tokenize.NUMBER:
                yield int(tokval)
            elif toknum in [tokenize.OP, tokenize.STRING, tokenize.NAME]:
                yield tokval
            elif toknum == tokenize.ENDMARKER:
                break
            else:
                raise RuntimeError("Unknown token %s: '%s'" %
                                   (tokenize.tok_name[toknum], tokval))
    
    
    def constant_fold(code):
        """Constant-folds simple mathematical expressions like 2 3 + to 5."""
        while True:
            # Find two consecutive numbers and an arithmetic operator
            for i, (a, b, op) in enumerate(zip(code, code[1:], code[2:])):
                if isinstance(a, int) and isinstance(b, int) \
                    and op in {
       "+", "-", "*", "/"}:
                    m = Machine((a, b, op))
                    m.run()
                    code[i:i+3] = [m.top()]
                    print("Constant-folded %s%s%s to %s" % (a, op, b, m.top()))
                    break
            else:
                break
        return code
    
    
    def repl():
        print('Hit CTRL-D or type "exit" to quit.')
    
        while True:
            try:
                source = input("> ")
                code = list(parse(source))
                code = constant_fold(code)
                Machine(code).run()
            except (RuntimeError, IndexError) as e:
                print("IndexError: %s" % e)
            except KeyboardInterrupt:
                print("\nKeyBoardInterrupt")
    
    if __name__ == "__main__":
        # Machine([
        # '"Enter a number: "', "print", "read", "cast_int",
        # '"Enter another number: "', "print", "read", "cast_int",
        # "over", "over",
        # '"Their sum is: "', "print", "+", "println",
        # '"Their product is: "', "print", "*", "println"
        # ]).run()
    
        # Machine([
        # '"Enter a number: "', "print", "read", "cast_int",
        # '"The number "', "print", "dup", "print", '" is "', "print",
        # 2, "%", "==", '"even."', '"odd."', "if", "println",
        # 0, "jmp" # loop forever!
        # ]).run()
        repl()

程序的运行结果:  
![这里写图片描述][SouthEast]

[http_www.ituring.com.cn_article_199660]: http://www.ituring.com.cn/article/199660
[SouthEast]: /images/20220608/ff7575ffe8be4223bdef297b65277a01.png