树的运用-计算器-Toy模板网

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实验要求

树的应用：计算器

要求：计算器需要实现所有单击版计算器所具有的功能，并要用到树结构。

代码实现

import re
from tkinter import *

from lark import Lark

grammar = """
    ?start: sum
    ?sum: product
        | sum "+" product   -> add
        | sum "-" product   -> sub
    ?product: atom
        | product "*" atom  -> mul
        | product "÷" atom  -> div
    ?atom: NUMBER           -> number
        | "-" atom         -> neg
        | "(" sum ")"
        | atom "%"          -> percentage
    %import common.CNAME
    %import common.NUMBER
    %import common.WS
    %ignore WS
"""


class Calculator:
    def __init__(self, master):
        self.master = master
        master.title("Calculator")

        self.parser = Lark(grammar, start='start')

        self.display = Entry(master, width=25, font=('Arial', 16))
        self.display.grid(row=0, column=0, columnspan=4, padx=5, pady=5)

        self.display_result = Entry(master, width=25, font=('Arial', 16))
        self.display_result.grid(row=1, column=0, columnspan=4, padx=5, pady=5)

        buttons = [['C', '↼', '^', '÷'],
                   ['7', '8', '9', '*'],
                   ['4', '5', '6', '-'],
                   ['1', '2', '3', '+'],
                   ['%', '0', '.', '='], ]

        for i in range(len(buttons)):
            for j in range(len(buttons[i])):
                self.create_button(buttons[i][j], i + 2, j)

    def create_button(self, text, row, column):
        button = Button(self.master, text=text, width=5, height=2, font=('Arial', 16),
                        command=lambda: self.click(text))
        button.grid(row=row, column=column, padx=5, pady=5)

    def click(self, key):
        if key == '=':
            try:
                expression = self.display.get()
                if re.search(r'\^', expression):
                    result = eval(expression)
                else:
                    tree = self.parser.parse(expression)
                    result = self.evaluate(tree)
                self.display_result.delete(0, END)
                self.display_result.insert(END, result)
            except:
                self.display_result.delete(0, END)
                self.display_result.insert(END, 'Error')
        elif key == 'C':
            self.display.delete(0, END)
            self.display_result.delete(0, END)
        elif key == '↼':
            last_index = self.display.index(END) - 1
            self.display.delete(last_index)
        else:
            self.display.insert(END, key)

    def evaluate(self, tree):
        if tree.data == 'number':
            return float(tree.children[0])
        elif tree.data == 'add':
            return self.evaluate(tree.children[0]) + self.evaluate(tree.children[1])
        elif tree.data == 'sub':
            return self.evaluate(tree.children[0]) - self.evaluate(tree.children[1])
        elif tree.data == 'mul':
            return self.evaluate(tree.children[0]) * self.evaluate(tree.children[1])
        elif tree.data == 'div':
            return self.evaluate(tree.children[0]) / self.evaluate(tree.children[1])
        elif tree.data == 'neg':
            return -self.evaluate(tree.children[0])
        elif tree.data == 'percentage':
            return self.evaluate(tree.children[0]) / 100.0


root = Tk()
calculator = Calculator(root)
root.mainloop()