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

Question

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?

Answer 1

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!