此行中的 setattr() 用法

Question

我从某个地方得到了这段代码，但我不明白这一行：

Dropdown.bind(on_select = lambda instance, x: setattr(mainbutton, 'text', x))

import kivy
from kivy.app import App
kivy.require("1.9.2")
from kivy.uix.dropdown import DropDown
from kivy.uix.button import Button
from kivy.base import runTouchApp
Dropdown = DropDown()
# creating an object out of a function
for i in range(1, 11):
    button = Button(text="Button Number " + str(i), size_hint_y=None, height=40)
    # 10 buttons with different numbers created
    button.bind(on_release=lambda button: Dropdown.select(button.text))
    # Dropdown is a function so that's why we're using Dropdown and not mainbutton that has no attribute 'select'
    # buttons bind to dropdown and if they're selected their text goes on dropdown main button
    # lambda for WHENEVER button is pressed, then when it's released something happens
    Dropdown.add_widget(button)
    # means that it is added on the layout and screen

mainbutton = Button(text="Select A Button", size_hint=(None, None), pos=(350, 300))

mainbutton.bind(on_release = Dropdown.open)
# when button is pressed and then it's released, dropdown menu opens
Dropdown.bind(on_select = lambda instance, x: setattr(mainbutton, 'text', x))
# 
runTouchApp(mainbutton)

Answer 1

Ok, so I don't know kivy and its not clear from the documentation that I can find, but it seems to me that kivy produces events internally and you can hook into them by binding a function of your own (a lambda in this case ) 到那个事件。

因此，当on_select事件发生时，使用两个参数调用 function。 这些是instance, x部分。 无论调用您的 function 都提供两个参数： instance是下拉实例， x是选择的数据。 您的lambda然后运行表达式： setattr(mainbutton, 'text', x)我认为它与mainbutton.text = x相同。