tkinter find

[Gigs_]

I want to make find in my text editor like in mozilla firefox on the bottom of my gui

this is only for learning.

class MyClass(Frame):
    def onFind(self, target=None):
        if target == None:
            target = tkSimpleDialog.askstring('Find!', 'Search for string!')
        if target:
            where = self.text.search(target, INSERT, END)
            if where:
                pastit = where + ('+%dc' % len(target))
                self.text.tag_remove(SEL, '1.0', END)
                self.text.tag_add(SEL, where, pastit)
                self.text.mark_set(INSERT, pastit)
                self.text.see(INSERT)
                self.text.focus()

    def findToolbar(self):
        frm = Frame(self.master)
        frm.pack(side=BOTTOM, expand=YES, fill=X)
        Button(frm, text='Quit!').pack(side=LEFT)
        e = Entry(frm)
        e.pack(side=LEFT)
        e.focus_set()
        target = e.get()
        b = Button(frm, text='find', command=lambda: self.onFind(target))
        b.pack(side=LEFT)

How to make when I open find toolbar that i dont have possibiliti to open the toolbar again when first is opened.
It seems that I cant get text from Entry, my target is empty