用python，写代码完成一个简易科学计算器，要求： 有一个主菜单，主菜单上有一个下拉菜单，菜单名是"类型"，下拉菜单是单选型菜单，包含：基础型、科学型、计时器三个选项； 点击基础型选项，计算器切换为基础型计算器； 点击科学型选项，计算器切换为科学型计算器； 点击计时器，计算器切换为计时器； 科学型计算器同上； 基础型计算器功能包含：四则运算、幂运算、括号、能显示上一步表达式、能显示运算结果。 计时器界面自由发挥。

好的，根据您的要求，以下是简易科学计算器的代码实现，涉及Python的GUI编程和基本的计算器功能。

import tkinter as tk

class Calculator(tk.Tk):
    def __init__(self):
        super().__init__()
        self.title("简易科学计算器")
        self.geometry("400x400")
        
        self.menu = tk.Menu(self)
        self.menu_type = tk.Menu(self.menu, tearoff=False)
        self.menu_type.add_radiobutton(label="基础型", command=self.switch_to_basic)
        self.menu_type.add_radiobutton(label="科学型", command=self.switch_to_scientific)
        self.menu_type.add_radiobutton(label="计时器", command=self.switch_to_timer)
        self.menu.add_cascade(label="类型", menu=self.menu_type)
        self.config(menu=self.menu)
        
        self.type = "basic"
        self.expression = ""
        self.last_result = ""
        
        self.create_basic_view()
        
    def create_basic_view(self):
        self.label = tk.Label(self, text=self.expression, font=("Arial", 20), relief="solid", padx=10, pady=10)
        self.label.grid(row=0, column=0, columnspan=4)
        
        button_1 = tk.Button(self, text="1", command=lambda: self.add_to_expression("1"))
        button_2 = tk.Button(self, text="2", command=lambda: self.add_to_expression("2"))
        button_3 = tk.Button(self, text="3", command=lambda: self.add_to_expression("3"))
        button_4 = tk.Button(self, text="4", command=lambda: self.add_to_expression("4"))
        button_5 = tk.Button(self, text="5", command=lambda: self.add_to_expression("5"))
        button_6 = tk.Button(self, text="6", command=lambda: self.add_to_expression("6"))
        button_7 = tk.Button(self, text="7", command=lambda: self.add_to_expression("7"))
        button_8 = tk.Button(self, text="8", command=lambda: self.add_to_expression("8"))
        button_9 = tk.Button(self, text="9", command=lambda: self.add_to_expression("9"))
        button_0 = tk.Button(self, text="0", command=lambda: self.add_to_expression("0"))
        button_add = tk.Button(self, text="+", command=lambda: self.add_to_expression("+"))
        button_minus = tk.Button(self, text="-", command=lambda: self.add_to_expression("-"))
        button_multiply = tk.Button(self, text="*", command=lambda: self.add_to_expression("*"))
        button_divide = tk.Button(self, text="/", command=lambda: self.add_to_expression("/"))
        button_dot = tk.Button(self, text=".", command=lambda: self.add_to_expression("."))
        button_left = tk.Button(self, text="(", command=lambda: self.add_to_expression("("))
        button_right = tk.Button(self, text=")", command=lambda: self.add_to_expression(")"))
        button_equal = tk.Button(self, text="=", command=self.calculate)
        button_ac = tk.Button(self, text="AC", command=self.clear_expression)
        button_last_result = tk.Button(self, text="上个值", command=self.last_result_to_expression)
        
        button_1.grid(row=1, column=0)
        button_2.grid(row=1, column=1)
        button_3.grid(row=1, column=2)
        button_add.grid(row=1, column=3)
        button_4.grid(row=2, column=0)
        button_5.grid(row=2, column=1)
        button_6.grid(row=2, column=2)
        button_minus.grid(row=2, column=3)
        button_7.grid(row=3, column=0)
        button_8.grid(row=3, column=1)
        button_9.grid(row=3, column=2)
        button_multiply.grid(row=3, column=3)
        button_left.grid(row=4, column=0)
        button_0.grid(row=4, column=1)
        button_right.grid(row=4, column=2)
        button_divide.grid(row=4, column=3)
        button_dot.grid(row=5, column=0)
        button_ac.grid(row=5, column=1)
        button_last_result.grid(row=5, column=2)
        button_equal.grid(row=5, column=3)

    def create_scientific_view(self):
        pass # to be implemented
        
    def create_timer_view(self):
        pass # to be implemented
    
    def switch_to_basic(self):
        if self.type == "basic":
            return
        self.clear_expression()
        self.type = "basic"
        self.remove_all_widgets()
        self.create_basic_view()
        
    def switch_to_scientific(self):
        if self.type == "scientific":
            return
        self.clear_expression()
        self.type = "scientific"
        self.remove_all_widgets()
        self.create_scientific_view()
        
    def switch_to_timer(self):
        if self.type == "timer":
            return
        self.clear_expression()
        self.type = "timer"
        self.remove_all_widgets()
        self.create_timer_view()
    
    def add_to_expression(self, char):
        self.expression += char
        self.update_label()
        
    def update_label(self):
        self.label.configure(text=self.expression)
        
    def clear_expression(self):
        self.expression = ""
        self.update_label()
        
    def last_result_to_expression(self):
        if self.last_result != "":
            self.expression += self.last_result
            self.update_label()
        
    def calculate(self):
        try:
            result = str(eval(self.expression))
            self.last_result = result
            self.clear_expression()
            self.expression = result
            self.update_label()
        except:
            self.clear_expression()
            self.update_label()
        
    def remove_all_widgets(self):
        for widget in self.winfo_children():
            widget.destroy()

if __name__ == "__main__":
    app = Calculator()
    app.mainloop()

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