Python Tkinter Entry.get() gives previous input-CodePudding

I am working on a relatively large project, but have managed to recreate my problem in just a few lines:

import tkinter as tk
    
root = tk.Tk()
root.geometry('200x200')
    
def doStuff():
    pass
sv = tk.StringVar()
def callback():
    print(E.get())
    doStuff()
    return True
    
E = tk.Entry(root, bg="white", fg="black", width=24, textvariable=sv, validate="key",validatecommand=callback)
E.grid(row=0, column=0, padx=30, pady=5, sticky=tk.E)
root.mainloop()

The desired output would be that every time the user changes the entry in this Entrywidget, a function is called. This works just fine, but using E.get() returns the 'previous' entry, for example:
-entry is 'boo'
-E.get() is 'bo'
Python seems to run Callback() before the Entry Widget has been changed.

CodePudding user response：

Validation by design happens before the text has been inserted or deleted. For validation to work, it must be able to prevent the data from being changed.

If you aren't doing validation, but instead just want to call a function when the value changes, the best way to do that is to put a trace on the associated variable.

def callback(*args):
    print(E.get())
    doStuff()
    return True
sv = tk.StringVar()
sv.trace_add("write", callback)