Python Tkinter：按钮点击赋值变量后无法返回值的问题求助

你定义的selection是每个函数内部的局部变量，函数执行结束后这个变量就会被销毁，外部无法访问；而且Tkinter按钮的command回调不会处理函数的返回值，所以就算你给函数加return selection也没用。

以下是三种可行的修改方式，按需选择：

方案1：使用全局变量 #

在函数内部声明selection为全局变量，这样修改的是全局作用域的变量，外部代码可以直接访问：

import tkinter as tk

selection = ""  # 定义全局变量

def select1():
    global selection
    selection = "General Knowledge"
    print(selection)

def select2():
    global selection
    selection = "Science"

def select3():
    global selection
    selection = "Entertainment"

def select4():
    global selection
    selection = "Miscellaneous"

root = tk.Tk()

button1 = tk.Button(text="General Knowledge", command=select1)
button1.place(x=100, y=100)

button2 = tk.Button(text="Science", command=select2)    
button2.place(x=100, y=140)

button3 = tk.Button(text="Entertainment", command=select3)
button3.place(x=100, y=180)

button4 = tk.Button(text="Miscellaneous", command=select4)
button4.place(x=100, y=220)

root.mainloop()

# 后续调用API时直接使用全局的selection变量
# 示例：call_api(selection)

方案2：用Lambda简化代码 #

不用写四个重复的函数，直接通过Lambda表达式在按钮的command参数里设置全局变量，代码更简洁：

import tkinter as tk

selection = ""

root = tk.Tk()

button1 = tk.Button(text="General Knowledge", command=lambda: globals().update(selection="General Knowledge"))
button1.place(x=100, y=100)

button2 = tk.Button(text="Science", command=lambda: globals().update(selection="Science"))    
button2.place(x=100, y=140)

button3 = tk.Button(text="Entertainment", command=lambda: globals().update(selection="Entertainment"))
button3.place(x=100, y=180)

button4 = tk.Button(text="Miscellaneous", command=lambda: globals().update(selection="Miscellaneous"))
button4.place(x=100, y=220)

root.mainloop()

方案3：面向对象封装（推荐） #

把窗口和变量封装成类，用实例属性存储selection，避免全局变量带来的混乱，更适合大型程序：

import tkinter as tk

class App:
    def __init__(self, root):
        self.root = root
        self.selection = ""  # 实例属性
        
        button1 = tk.Button(text="General Knowledge", command=lambda: self.set_selection("General Knowledge"))
        button1.place(x=100, y=100)
        
        button2 = tk.Button(text="Science", command=lambda: self.set_selection("Science"))    
        button2.place(x=100, y=140)
        
        button3 = tk.Button(text="Entertainment", command=lambda: self.set_selection("Entertainment"))
        button3.place(x=100, y=180)
        
        button4 = tk.Button(text="Miscellaneous", command=lambda: self.set_selection("Miscellaneous"))
        button4.place(x=100, y=220)
    
    def set_selection(self, value):
        self.selection = value
        print(self.selection)
        # 可以在这里直接调用API，比如：self.call_api()
    
    def call_api(self):
        # 这里编写调用API的逻辑，使用self.selection即可
        print(f"调用API，分类：{self.selection}")

if __name__ == "__main__":
    root = tk.Tk()
    app = App(root)
    root.mainloop()
    
    # 程序结束后仍可访问选择结果
    print(f"最终选择：{app.selection}")

内容的提问来源于stack exchange，提问作者callumgilf