来自文档：
w.winfo_width()
Returns the current width of w in pixels. See the remarks on geometry
updating under .winfo_geometry(), above. You may prefer to use the
.winfo_reqwidth() method, described above; it is always up to date.
不是根据我的经验。每次单击标签后，以下程序将打印相同值两次。该值逐行变化。
from Tkinter import *
root = Tk()
t = "a label"
padx = 0
f = Frame(root, padx=padx, bg='red')
l = Label(f, text=t, bg='yellow')
def cb(e):
global t, padx
w = f.winfo_reqwidth()
print w,
t = t + 'x'
padx += 10
f.configure(padx=padx)
l.configure(text=t)
#f.update_idletasks()
w = f.winfo_reqwidth()
print w
f.place(x=0,y=0)
l.pack()
l.bind('<Button-1>', cb)
mainloop()
打印：
49 49
76 76
103 103
取消注释f.update_idletasks行并打印：
49 76
76 103
103 130
文档错了吗？我读错了吗？有没有办法在更改后立即检索小部件所需的宽度和高度？