Python tkinter Entry小部件无值

Question

I am reading from a database and I am using ttk.Entry widgets to display the database data. I want the user to see the values and if they want to, change them.

But when a database's value is Null ( None value for Python) the Entry widget displays the word "None" and not a None value. Is there any way to have a None value at the Entry widget or I have to compare using the word "None" hoping that the user will not use it?

The code just shows the Entry display of a "None" value:

from tkinter import *
from tkinter import ttk

root = Tk()

entry_value = StringVar()
entry = ttk.Entry(root, textvariable=entry_value)
entry.pack(padx=10, pady=10)
ttk.Button(root, text='Exit', command=root.destroy).pack(padx=10, pady=10)

myvalue = None
entry_value.set(myvalue)
print('same values') if myvalue == entry_value.get() else print('different values')
print('myvalue is None') if myvalue is None else print('myvalue is not None')
print('entry_value is None') if entry_value.get() is None else print('entry_value is not None')
print('entry_value is the word None') if entry_value.get() == 'None' else print ('entry_value is not thr word None')

root.mainloop()

Answer 1

Tkinter widgets cannot represent the value None . Tkinter is just a thin python wrapper around a tcl interepter, and the tcl language has no notion of None or a null value. Since str(None) returns the string "None" , that is what the widget is set to when you give it the value of None .

You'll have to come up with some custom way to handle that yourself, such as inserting an empty string if the value is actually None .