Python Tkinter Scrollable Text，滑块不会出现

我'm trying to make a scrollable Text with tkinter widget. I want the scrollbar to appear only when I need it ( when a part of my text widget can' t可见） .
我的程序会搜索每个打字，如果它不是's the case or not, if it is the scrollbar appears, if it' .
它第一次运行良好，但如果我擦除一些文本（所以滚动条消失），然后写一些，滚动条出现但没有滑块！

#-*-coding:latin-1-*

from tkinter import *


class TextScrollbar(Frame):
    """
       A Text widget which can be scrolled.
       Text widget with a scrollbar appearing only when you need it
       (when there is text that you can see)
       Use self.Text to acccess to your Text widget
    """

    def __init__( self, master=None, cnf={}, **kw ):

        #Creat a Frame which will contain the Text and the Scrollbar widget
        Frame.__init__( self, master=None, cnf={}, **kw )

        #Creat Scrollbar widget
        self.ScrollBar=Scrollbar( self, orient='vertical' )

        #Creat Text widget
        self.Text=Text(self, cnf={}, **kw)

        #Link between Text and Scrollbar widgets
        self.Text.config( yscrollcommand=self.ScrollBar.set )
        self.ScrollBar.config( command=self.Text.yview )      

        #Distribution of the Text widget in the frame
        self.Text.pack( side='left', fill=BOTH, expand=1 )


        def _typing(event):
            """Check whether you need a scrollbar or not"""
            if Text.ScrollBar.get()==(0.0, 1.0):
                self.ScrollBar.pack_forget()
            else:
                self.ScrollBar.pack( side='right', fill=Y, expand=1 )

        self.Text.bind('<Key>',_typing)



root=Tk()
Text=TextScrollbar(root)
Text.pack(fill=BOTH, expand=1)

First trial

Second trial

I still don't know why it didn't work but replacing .pack methode by .grid methode it works, here is the code updated

#-*-coding:latin-1-*

from tkinter import *


class TextScrollbar(Frame):
    """
       A Text widget which can be scrolled.
       Text widget with a scrollbar appearing only when you need it
       (when there is text that you can see)
       Use self.Text to acccess to your Text widget
    """

    def __init__( self, master=None, cnf={}, **kw ):

        #Creat a Frame which will contain the Text and the Scrollbar widget
        Frame.__init__( self, master=None, cnf={}, **kw )
        self.grid_columnconfigure( 0, weight=1 )
        self.grid_rowconfigure( 0, weight=1 )

        #Creat Scrollbar widget
        self.Scrollbar=Scrollbar( self, orient='vertical' )

        #Creat Text widget
        self.Text=Text( self, cnf={}, **kw )

        #Link between Text and Scrollbar widgets
        self.Text.config( yscrollcommand=self.Scrollbar.set )
        self.Scrollbar.config( command=self.Text.yview )      

        #Distribution of the Text widget in the frame
        self.Text.grid( row=0, column=0, sticky=N+S+E+W )



        def TypingAndResizing(event):
            """Check whether you need a scrollbar or not"""
            if Text.Scrollbar.get()==(0.0, 1.0):
                self.Scrollbar.grid_forget()
            else:
                self.Scrollbar.grid( row=0, column=1, sticky=S+N )

        self.Text.bind( '<KeyRelease>', TypingAndResizing )
        self.Text.bind( '<Configure>', TypingAndResizing )



root=Tk()
Text=TextScrollbar(root)
Text.pack(fill=BOTH, expand=1)