AttributeError:“NoneType”对象没有属性“\u root”

Question

我对Python 3完全不熟悉，只是在YouTube上做了一些简单的练习。

https://www.youtube.com/watch?v=nefopNkZmB4&index=3&list=PL6gx4Cwl9DGAcbMi1sH6oAMk4JHw91mC_

这是我的代码：

    from tkinter import *


def iCalc(source, side):
    storeObj = Frame(source, borderwidth=4, bd=4, bg="powder blue")
    storeObj.pack(side=side, expand=YES, fill=BOTH)
    return storeObj


def button(source, side, text, command=None):
    storeObj = Button(source, text=text, command=command)
    storeObj.pack(side=side, expand=YES, fill=BOTH)
    return storeObj


class app(Frame):

    def __init__(self):
        Frame.__init__(self)
        self.option_add('*Font', 'arial 20 bold')
        self.pack(expand=YES, fill=BOTH)
        self.master.title('Calculator')

    display = StringVar()
    Entry(self, relief=RIDGE, textvariable=display, justify='right', bd=30, bg="powder blue").pack(side=TOP, expand=YES,
                                                                                                   fill=BOTH)
for clearBut in (["CE"], ["C"]):
    erase = iCalc(self, TOP)
for ichar in clearBut:
    button(erase, LEFT, ichar,
           lambda storeObj=display, q=ichar: storeObj.set(''))

for NumBut in ("789/", "456*", "123-", "0.+"):
    FunctionNum = iCalc(self, TOP)
for iEquals in NumBut:
    button(FunctionNum, LEFT, iEquals,
           lambda storeObj=display, q=iEquals: storeObj.set(storeObj.get() + q))
EqualsButton = iCalc(self, TOP)
for iEquals in '=':
    if iEquals in "=":
        btniEquals = button(EqualsButton, LEFT, iEquals)
        btniEquals.bind('<ButtonRelease-1>',
                        lambda e, s=self, storeObj=display: s.calc(storeObj), '+')
else:
    btniEquals = button(EqualsButton, LEFT, iEquals,
                        lambda storeObj=display, s=' %s ' % iEquals: storeObj.set(storeObj.get() + s))


def calc(self, display):
    try:
        display.set(eval(display.get()))
    except:
        display.set("ERROR")

if __name__ == '__main__':
    app().mainloop()

我得到错误：

我做错什么了？

Answer 1

由于缩进，display = StringVar()不在方法中。这意味着在第一次定义类时执行它。在创建根窗口之前，不能创建StringVar的实例。

您需要为该行及其下面的行再添加一个缩进级别。