Question

I’m writing some code in python and I’m having trouble when trying to retrieve content of an Entry widget. The thing is: I want to limit the characters that can be typed, so I’m trying to clear the Entry widget when I reach the specific number of characters (2 in this case), but it looks like I always miss the last typed character. I added the lost character in a print to show.

Here’s the sample code:

from Tkinter import * class sampleFrame:     def __init__(self, master):         self.__frame = Frame(master)         self.__frame.pack()     def get_frame(self):         return self.__frame   class sampleClass:     def __init__(self, master):         self.__aLabel = Label(master,text='aLabel', width=10)         self.__aLabel.pack(side=LEFT)         self.__aEntry = Entry (master, width=2)         self.__aEntry.bind('<Key>', lambda event: self.callback(event, self.__aEntry))         self.__aEntry.pack(side=LEFT)      def callback(self, event, widgetName):         self.__value = widgetName.get()+event.char         print self.__value         if len(self.__value)>2:             widgetName.delete(2,4)      root = Tk() aSampleFrame = sampleFrame(root) aSampleClass = sampleClass(aSampleFrame.get_frame()) root.mainloop() 

Any help will be much appreciated!

Thanks in advance

Answer 1

At first, after you do the deletion, the event goes on with its normal processing, i.e. the character gets inserted. You need to signal to Tkinter that the event should be ignored.

So in your code above, add the marked line:

if len(self.__value) > 2:     widgetName.delete(2,4)     return 'break' # add this line 

On the other hand, why do you go through the lambda? An event has a .widget attribute which you can use. So you can change your code into:

    self.__aEntry.bind('<Key>', self.callback) # ※ here!     self.__aEntry.pack(side=LEFT)  def callback(self, event):     self.__value = event.widget.get()+event.char # ※ here!     print self.__value     if len(self.__value)>2:         event.widget.delete(2,4) # ※ here!         return 'break' 

All the changed lines are marked with ‘here!’