Das deutsche Python-Forum

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eingabe = Entry(root,background='yellow',foreground='blue',font='courier',width=4)         ## Eingabezeile erzeugen
eingabe.pack()## und anzeigen

##  und beim lesen begrenzen ///// eingabe.delete(4,END)

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#!/usr/bin/env python
import Tkinter as tk


class MaxLengthEntry(tk.Entry):
    def __init__(self, master, max_length, textvariable=None, **args):
        self.max_length = max_length
        self._textvariable = textvariable
        if self._textvariable is None:
            self._textvariable = tk.StringVar()
        self._old_value = self._textvariable.get()
        self._textvariable.trace('w', self.validate)
        tk.Entry.__init__(self,
                          master,
                          textvariable=self._textvariable,
                          width=max_length,
                          **args)
    
    def validate(self, *args):
        text = self.get()
        if len(text) <= self.max_length:
            self._old_value = text
        else:
            self._textvariable.set(self._old_value)


def main():
    root = tk.Tk()
    entry = MaxLengthEntry(root, 4)
    entry.pack()
    root.mainloop()


if __name__ == '__main__':
    main()

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self._textvariable.trace('w', self.validate)

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>>> import Tkinter
>>> root = Tkinter.Tk()
>>> print dir(Tkinter.StringVar())
['__del__', '__doc__', '__eq__', '__init__', '__module__', '__str__', '_default', '_master', '_name', '_tk', 'get', 'set', 'trace', 'trace_variable', 'trace_vdelete', 'trace_vinfo']