Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
292 views
in Technique[技术] by (71.8m points)

python 3.x - what is the difference between a variable and StringVar() of tkinter

Code:

import tkinter as tk
a = "hi"
print(a)
a1 = tk.StringVar()
a1.set("Hi")
print(a1)

Output:

hi ##(Output from first print function) 

AttributeError: 'NoneType' object has no attribute '_root' (Output from second print function) 

My question:

What is the difference between a and a1 in above code and their use-cases. Why a1 is giving error?

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

A StringVar() is used to edit a widget's text

For example:

import tkinter as tk


root = tk.Tk()
my_string_var = tk.StringVar()
my_string_var.set('First Time')
tk.Label(root, textvariable=my_string_var).grid()
root.mainloop()

Will have an output with a label saying First Time NOTE:textvariable has to be used when using string variables

And this code:

import tkinter as tk

def change():
    my_string_var.set('Second Time')

root = tk.Tk()
my_string_var = tk.StringVar()
my_string_var.set('First Time')
tk.Label(root, textvariable=my_string_var).grid()
tk.Button(root, text='Change', command=change).grid(row=1)
root.mainloop()

Produces a label saying First Time and a button to very easily change it to Second Time.

A normal variable can't do this, only tkinter's StringVar()

Hopes this answers your questions!


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...