多重继承在python中不起作用

Question

我正在做一个 GUI 格式的 bmi 计算器作为学校项目。

这是代码：

from tkinter import *
import tkinter.font as tkfont

class App(Tk):
    def __init__(self, *args, **kwargs):
        Tk.__init__(self, *args, **kwargs)
        #Setup menu here
        MainMenu(self)
        # Setup Frame
        container = Frame(self)
        container.pack(side="top", fill="both", expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.columnconfigure(0, weight=1)

        self.frames = {}

        for F in (StartPage, PageOne, PageTwo, ResultPageOne, ResultPageTwo):
            frame = F(container, self)
            self.frames[F] = frame
            frame.grid(row=0, column=0, sticky="nsew")
        
        self.show_frame(StartPage)
    def show_frame(self, context):
        frame = self.frames[context]
        frame.tkraise()
class StartPage(Frame):
    def __init__(self, parent, controller):
        Frame.__init__(self, parent)
        fontstyle = tkfont.Font(family="Helvetica", size=30)

        label = Label(self, text="BMI CALCULATOR",font=fontstyle)
        label.pack(padx=10, pady=10)

        go_to_metric = Button(self, text="Measure in Metric values", command=lambda:controller.show_frame(PageOne), width=30)
        go_to_metric.pack(side=LEFT)

        go_to_english = Button(self, text="Measure in English values", command=lambda:controller.show_frame(PageTwo), width=30)
        go_to_english.pack(side=LEFT)   
class PageOne(Frame):
    def __init__(self, parent, controller):
        Frame.__init__(self, parent)

        label = Label(self, text="Measure BMI in metric values")
        label.pack(padx=10, pady=10)

        Label(self, text="Height in centimeters (decimal points allowed):").pack()
        height_in_cm = Entry(self)
        height_in_cm.pack()
        Label(self, text="Weight in Kilograms (decimal points allowed)").pack()
        weight_in_kg = Entry(self)
        weight_in_kg.pack()
        
        height_in_cm = height_in_cm.get()
        weight_in_kg = weight_in_kg.get()


        Button(self, text="Calculate", command=lambda:controller.show_frame(ResultPageOne)).pack()

        page_two = Button(self, text="Measure in English values", command=lambda:controller.show_frame(PageTwo))
        page_two.pack()

        def calculate_bmi(self):
            height_in_m = self.height_in_cm/100
            final_height = height_in_m**2
            bmi = self.weight_in_kg/final_height
            return bmi

class PageTwo(Frame):
    def __init__(self, parent, controller):
        Frame.__init__(self, parent)

        label = Label(self, text="Measure BMI in English values")
        label.pack(padx=10, pady=10)

        Label(self, text="Height in Inches (decimal points allowed):").pack()
        height_in_in = Entry(self)
        height_in_in.pack()
        Label(self, text="Weight in Pounds (decimal points allowed)").pack()
        weight_in_lbs = Entry(self)
        weight_in_lbs.pack()

        height_in_in = height_in_in.get()
        weight_in_lbs = weight_in_lbs.get()

        Button(self, text="Calculate", command=lambda:controller.show_frame(ResultPageTwo)).pack()

        page_one = Button(self, text="Measure in Metric values", command=lambda:controller.show_frame(PageOne))
        page_one.pack()
        def calculate_bmi(self):
            final_height = self.height_in_in**2
            bmi = self.weight_in_lbs/final_height*703
            return bmi

class ResultPageOne(Frame, PageOne):
    def __init__(self, parent, controller):
        Frame.__init__(self, parent)
        fontstyle = tkfont.Font(family="Helvetica", size=30)
        label = Label(self,text="Results", font=fontstyle)
        label.pack()



class ResultPageTwo(Frame, PageTwo):
    def __init__(self, parent, controller):
        Frame.__init__(self, parent)
        fontstyle = tkfont.Font(family="Helvetica", size=30)
        label = Label(self, text="Results 2", font=fontstyle)
        label.pack()

class MainMenu:
    def __init__(self,master):
        menubar = Menu(master)
        filemenu = Menu(menubar, tearoff=0)
        filemenu.add_command(label="Exit", command=master.quit)
        menubar.add_cascade(label="File",menu=filemenu)
        master.config(menu=menubar)

app = App()
app.mainloop()

我想在两个类（即 PageOne 和 PageTwo）中采用 calculate_bmi 方法，并将它们继承到两个结果页面类中并显示结果。 但是当我运行代码时，就会出现这个错误：

Traceback（最近一次调用最后一次）： 文件“TN1.py”，第 92 行，在 类 ResultPageOne(Frame,PageOne): TypeError：无法创建一致的方法解析 基础框架、PageOne 的订单 (MRO)

Answer 1

section Bad Method Resolution Orders中描述了这种情况

如果 MRO 破坏了 局部优先顺序 和 单调性 等基本属性，则它是不好的。

>>> F=type('Food',(),{'remember2buy':'spam'})
>>> E=type('Eggs',(F,),{'remember2buy':'eggs'})
>>> G=type('GoodFood',(F,E),{}) # under Python 2.3 this is an error!

带继承图

             O
             |
(buy spam)   F
             | \
             | E   (buy eggs)
             | /
             G

     (buy eggs or spam ?)

真正的解决方案是设计一个明确的层次结构，即从 E 和 F（更具体的第一个）而不是从 F 和 E 派生 G；在这种情况下，毫无疑问，MRO 是 GEF。