正确的答案是，使用
validatecommand小部件的属性。不幸的是，尽管在
Tkinter中有足够的文档记录，但该功能在
Tkinter领域中的记录不足。即使没有很好地记录下来，它也具有验证所需的一切，而无需求助于绑定或跟踪变量，或在验证过程中修改小部件。
诀窍是要知道您可以让
Tkinter将特殊值传递给
validate命令。这些值为您提供了决定数据是否有效所需的所有信息：编辑之前的值，编辑之后的值（如果编辑有效）以及其他几位信息。但是，要使用这些命令，您需要做一点巫术，以使此信息传递到您的
validate命令。
注意：验证命令返回
True或至关重要
False。任何其他情况都会导致该小部件的验证被关闭。
这是一个仅允许小写的示例（并显示所有这些时髦的值）：
import tkinter as tk # python 3.x# import Tkinter as tk # python 2.xclass Example(tk.frame): def __init__(self, parent): tk.frame.__init__(self, parent) # valid percent substitutions (from the Tk entry man page) # note: you only have to register the ones you need; this # example registers them all for illustrative purposes # # %d = Type of action (1=insert, 0=delete, -1 for others) # %i = index of char string to be inserted/deleted, or -1 # %P = value of the entry if the edit is allowed # %s = value of entry prior to editing # %S = the text string being inserted or deleted, if any # %v = the type of validation that is currently set # %V = the type of validation that triggered the callback # (key, focusin, focusout, forced) # %W = the tk name of the widget vcmd = (self.register(self.onValidate), '%d', '%i', '%P', '%s', '%S', '%v', '%V', '%W') self.entry = tk.Entry(self, validate="key", validatecommand=vcmd) self.text = tk.Text(self, height=10, width=40) self.entry.pack(side="top", fill="x") self.text.pack(side="bottom", fill="both", expand=True) def onValidate(self, d, i, P, s, S, v, V, W): self.text.delete("1.0", "end") self.text.insert("end","OnValidate:n") self.text.insert("end","d='%s'n" % d) self.text.insert("end","i='%s'n" % i) self.text.insert("end","P='%s'n" % P) self.text.insert("end","s='%s'n" % s) self.text.insert("end","S='%s'n" % S) self.text.insert("end","v='%s'n" % v) self.text.insert("end","V='%s'n" % V) self.text.insert("end","W='%s'n" % W) # Disallow anything but lowercase letters if S == S.lower(): return True else: self.bell() return Falseif __name__ == "__main__": root = tk.Tk() Example(root).pack(fill="both", expand=True) root.mainloop()有关调用该
register方法时幕后情况的更多信息，请参见输入验证
tkinter
