Declare Stringvar variable as class variable in Python

Question

I want to initiate a class variable in order to pass it to another class. This variable has to be a StringVar variable as I want to use it for an Entry function of Tkinter. What I have done so far is this:

class ClassA:
    var1 = StringVar()
    def __init__(self,master):
        entry1 = Entry(master, textvariable = var1)

root = Tk()
my_gui = ClassA(root)
root.mainloop()

However, it gives the message:

StringVar instance has no attribute '_tk'.

This can be solved by adding Tk() before the declaration of StringVar but this produces a new window when I start my app. Is there a way to declare it without having to add the Tk() line? I can't figure out why this happens as I initiate Tk() outside the class.

Why exactly do you need it to be class variable as opposed to an instance variable? — Nae
– Nae, Commented Mar 16, 2018 at 10:22
"I want to initiate a class variable in order to pass it to another class." - it doesn't have to be a class variable in order for you to do that. — Bryan Oakley
– Bryan Oakley, Commented Mar 16, 2018 at 13:55
How else can I know the value of a StringVar from another class without it being a class variable? — tzoukritzou
– tzoukritzou, Commented Mar 18, 2018 at 18:12

Nae · Accepted Answer · 2018-03-16 10:33:47Z

3

Non-definition lines under a class declaration are read as soon as they're reached, and at the time at which the var1 = StringVar() there is no Tk instance, hence the error.

You can instead assign var1 class variable inside a method in the class, __init__ perhaps. Replace:

class ClassA:
    var1 = StringVar()
    def __init__(self,master):
        entry1 = Entry(master, textvariable = var1)

with:

class ClassA:
    def __init__(self,master):
        entry1 = Entry(master)
        ClassA.var1 = StringVar()
        entry1['textvariable'] = ClassA.var1

A complete example:

try:
    import tkinter as tk
except ImportError:
    import Tkinter as tk


class ClassA:
    def __init__(self, master):
        entry1 = tk.Entry(master)
        ClassA.var1 = tk.StringVar()
        entry1['textvariable'] = ClassA.var1
        ClassA.var1.set('"asd"')
        print("[Inside call], it is: {}".format(entry1.get()))


root = tk.Tk()
my_gui = ClassA(root)
print("[Outside call], it is: {}".format(ClassA.var1.get()))
tk.mainloop()

answered Mar 16, 2018 at 10:33

Nae

15.5k8 gold badges62 silver badges89 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

tzoukritzou Over a year ago

Using this example, when I want to use the StringVar from another class, it gives me the error: AttributeError: class ClassA has no attribute 'var1'.

Nae Over a year ago

@tzoukritzou With the example above, there has to be an instance of ClassA such as my_gui.

Collectives™ on Stack Overflow

Declare Stringvar variable as class variable in Python

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related