对象没有属性错误tkinter / python

Question

class DropdownList(object):

    def __init__(self, master):
        self.master = master
        self.mainFrame = Frame(self.master, padx=1, pady=1) # if defined here, when the code reaches the 'Label' function, the 'object has no attribute mainFrame' error appears
        self.mainFrame.pack()

    def heightQuestion(self, rowNumber, columnNumber):
        self.heightEntry = ''

        # self.mainFrame = Frame(self.master, padx = 1, pady = 1) - if defined here, the attribute can be used in all other methods as well
        # self.mainFrame.pack()
        Label(self.mainFrame, text = 'What is your height?', font=('Roboto', 20)).grid(row = rowNumber, column = columnNumber)
        Entry(self.mainFrame, textvariable = self.heightEntry, bd = 5, font = ('Roboto', 15)).grid(row = rowNumber+1, column = columnNumber)

如果我在构造函数中定义属性，则会收到“对象没有属性”错误。但是，如果我用其他方法（例如“ heightQuestion”）定义它，则可以正常工作。我希望在构造函数中定义属性。

错误：     Label（self.mainFrame，text ='您的身高是多少？'，font =（'Roboto'，20））。grid（row = rowNumber，column = columnNumber）    getattr 中的文件“ C：\ Users \ Marius \ AppData \ Local \ Programs \ Python \ Python36-32 \ lib \ tkinter__init __。py”，第2095行     返回getattr（self.tk，attr） AttributeError：“ _ tkinter.tkapp”对象没有属性“ mainFrame”