Python 3.4 Tkinter - 对象没有该属性

Question

我正在制作一个程序，想要模拟一个控制台。这是我到目前为止写的代码（我今天刚开始学习Tkinter，虽然我不确定Tkinter是否是最好的选择）：

from tkinter import *

class App:
    def __init__(self, master):
        self.frame = Frame(master, bg = 'black')
        self.bottomframe = Frame(master, bg = 'black')
        self.elabel = Label(master, text = '>', bg = 'black', font = 'system', fg = 'white')
        self.einput = Entry(master, bd =0, bg = 'black', font = 'system', fg = 'white', command = self.update_text())

        # Packing
        self.frame.pack()
        self.bottomframe.pack(side = BOTTOM)
        self.elabel.pack(side = LEFT)
        self.einput.pack(side = LEFT)
    def update_text(self):
        self.einput.insert(0, '>')


root = Tk()
app = App(root)
root.mainloop()

出现的错误是

Traceback (most recent call last):
  File "C:/Users/*/PycharmProjects/ConsoleDungeon/game.py", line 21, in <module>
    app = Game(root)
  File "C:/Users/*/PycharmProjects/ConsoleDungeon/game.py", line 9, in __init__
    self.einput = Entry(master, bd =0, bg = 'black', font = 'system', fg = 'white', command = self.update_text())
  File "C:/Users/*/PycharmProjects/ConsoleDungeon/game.py", line 17, in update_text
    self.einput.insert(0, '>')
AttributeError: 'Game' object has no attribute 'einput'

还有一件事：在这一行

self.einput = Entry(master, bd =0, bg = 'black', font = 'system', fg = 'white', command = self.update_text())

我不太确定如何使用command这个参数。

Answer 1

我不太确定在一个 Entry 组件上，command 参数应该做什么，但问题确实出在这里。command 需要一个可以调用的东西（也就是说，它需要一个函数的名字，而不是直接调用这个函数）。你现在程序的执行流程是：

create App
make App.frame
make App.bottomframe
make App.elabel
make App.einput
--> Oh, there's a function call in that declaration, gotta follow it before I
    finish making this object
------> The function call refers to an `App.einput`, but I don't have one of
        those (yet!) so we better throw an AttributeError