运行环境：python3.9+wxPython4.2.1
运行效果：
按下等于号，输出：
按下R键，保留两位小数

键盘布局与逻辑分离，添加删除功能一般功能或修改键盘布局只需要更改词典的顺序即可。添加特殊功能时则需要将队对应的逻辑也写一下。

import re
import wx


class MCalculator(wx.Frame):
    pos_x, pos_y = 10, 70
    btn_w, btn_h = 50, 50

    x_interval = 83
    y_interval = 83

    layout_dict = [
        {
            "C": "special",
            "➗": "operator[/]",
            "✖": "operator[*]",
            "⬅": "special"
        },
        {
            "7": "number",
            "8": "number",
            "9": "number",
            "➖": "operator[-]"
        },
        {
            "4": "number",
            "5": "number",
            "6": "number",
            "➕": "operator[+]"
        },
        {
            "1": "number",
            "2": "number",
            "3": "number",
            "＝": "special"
        },
        {
            "0": "number",
            ".": "number",
            "(": "operator[(]",
            ")": "operator[)]"
        },
        {
            "^": "operator[**]",
            "R": "special"
        }
    ]
    layout = None
    numbers = None
    operators = None

    @classmethod
    def initialize_class_attr(cls):
        regex_eq = r'operator\[(.*?)\]'
        cls.layout = [[c for c in cls.layout_dict[i]] for i in range(len(cls.layout_dict))]
        cls.numbers = [key for d in cls.layout_dict for key, value in d.items() if value == "number"]
        cls.operators = {
            key: re.search(regex_eq, value).group(1)
            for d in cls.layout_dict
            for key, value in d.items()
            if re.match(regex_eq, value)
        }
        pass

    def __init__(self):
        wx.Frame.__init__(self, None, title="简单计算器", pos=(100, 100), size=(340, 600))
        self.pl = wx.Panel(self, pos=(0, 0), size=(300, 600))
        # self.pl.SetBackgroundColour(wx.RED)
        self.entry = wx.TextCtrl(self.pl, pos=(10, 10), size=(300, 50), style=wx.TE_RIGHT | wx.TE_READONLY)

        self.btns = [[None for _ in range(len(self.layout[i]))] for i in range(len(self.layout))]

        self.special_function_dict = {
            "＝": self.On_btn_eq,
            "⬅": self.On_btn_back,
            "C": self.On_btn_clear,
            "R": self.On_do_round
        }

        for i in range(len(self.layout)):
            for j in range(len(self.layout[i])):
                # 创建按键
                self.btns[i][j] = wx.Button(
                    self.pl,
                    label=self.layout[i][j],
                    pos=(self.pos_x + j * self.x_interval, self.pos_y + i * self.y_interval),
                    size=(self.btn_w, self.btn_h))
                # 为数字键绑定事件
                if self.layout[i][j] in self.numbers:
                    self.Bind(
                        wx.EVT_BUTTON,
                        lambda _, lbl=self.layout[i][j]: self.entry.AppendText(lbl),
                        self.btns[i][j])
                # 为运算按键绑定事件
                if self.layout[i][j] in self.operators:
                    self.Bind(
                        wx.EVT_BUTTON,
                        lambda _, lbl=self.operators[self.layout[i][j]]: self.entry.AppendText(lbl),
                        self.btns[i][j])
                # 为其他特殊功能绑定事件
                if self.layout[i][j] in self.special_function_dict:
                    self.Bind(
                        wx.EVT_BUTTON,
                        self.special_function_dict[self.layout[i][j]],
                        self.btns[i][j])

    def Handle_exception(self, text, e):
        self.entry.SetValue(f"【算式：{text}】发生错误！{str(e)}")

    def On_btn_eq(self, event):
        text = ""
        try:
            text = self.entry.GetValue()
            result = str(eval(text))
            self.entry.SetValue(result)
        except Exception as e:
            self.Handle_exception(text, e)

    def On_btn_back(self, event):
        text = self.entry.GetValue()
        self.entry.SetValue(text[:-1])

    def On_btn_clear(self, event):
        self.entry.Clear()

    def On_do_round(self, event):
        text = ""
        try:
            text = self.entry.GetValue()
            result = str(round(float(text), 2))
            self.entry.SetValue(result)
        except Exception as e:
            self.Handle_exception(text, e)



if __name__ == '__main__':
    app = wx.App()
    MCalculator.initialize_class_attr()
    frame = MCalculator()
    frame.Show()
    app.MainLoop()