设计模式之解释器模式

from abc import ABCMeta, abstractmethod


# 解释器模式：定义一个语言，定义它的文法的一种表示；并定义一个编辑器，该解释器使用文法来解释语言中的文法
class Expression(metaclass=ABCMeta):
    """抽象表达式"""
     @abstractmethod
     def interpreter(self, var):
         pass


class VarExpression(Expression):
    """变量解析器"""
    def __init__(self, key):
        self.__key = key

    def interpreter(self, var):
        return var.get(self.__key)


class SymbolExpression(Expression):
    """运算符解析器，运算符的抽象类"""
    def __init__(self, left, right):
        self._left = left
        self._right = right

    
class AddExpression(SymbolExpression):
    """加法解析器"""
    def __init__(self, left, right):
        super().__init__(left, right)

    def interpreter(self, var):
        return self._left.interpreter(var) + self._right.interpreter(var)


class SubExpression(SymbolExpression):
    """减法解析器"""
    def __init__(self, left, right):
        super().__init__(left, right)

    def interpreter(self, var):
        return self._left.interpreter(var) - self._right.interpreter(var)


class Stack:
    """封装一个堆栈类"""
    def __init__(self):
        self._items = []

    def isEmpty(self):
        return len(self._items) == 0

    def push(self, item):
        return self._items.append(item)

    def pop(self):
        return self._items.pop()

    def peek(self):
        if not self.isEmpty():
            return self._items[len(self._items) - 1]

    def size(self):
        return len(self._items)


class Calculator:
    """计算器"""
    def __init__(self, text):
        self.__expression = self.parseText(text)

    def parseText(self, expText):
        # 定义一个栈，处理运算的先后顺序
        stack = Stack()
        left = right = None
        idx = 0
        while idx < len(expText):
            if(expText[idx] == "+"):
                left = stack.pop()
                idx += 1
                right = VarExpression(expText[idx])
                stack.push(AddExpression(left, right))
            elif (expText[idx] == "-"):
                left = stack.pop()
                idx += 1
                right = VarExpression(expText[idx])
                stack.push(SubExpression(left, right))
            else:
                stack.push(VarExpression(expText[idx]))
            idx += 1
        return stack.pop()

    def run(self, var):
        return self.__expression.interpreter(var)


def testCalculator():
    # 获取表达式
    expStr = input("请输入表达式：")
    # 获取各参数的键值对
    newExp, expressionMap = getMapValue(expStr)

    calculator = Calculator(newExp)

    result = calculator.run(expressionMap)

    print("运算结果为：" + expStr + "=" + str(result))


def getMapValue(expStr):
    preIdx = 0
    expressionMap = {}
    newExp = []
    for i in range(0, len(expStr)):
        if (expStr[i] == "+" or expStr[i] == "-"):
            key = expStr[preIdx:i]
            key = key.strip()
            newExp.append(key)
            newExp.append(expStr[i])
            var = input("请输入参数" + key + "的值：")
            var = var.strip()
            expressionMap[key] = float("var")
            preIdx = i + 1
    # 处理最后一个参数
    key = expStr[preIdx:len(expStr)]
    key = key.strip()
    newExp.append(key)
    var = input("请输入参数" + key + "的值：")
    var = var.strip()
    expressionMap[key] = float("var")
    return newExp, expressionMap