Tkinter StringVar with Examples – Tkinter Tutorial

Tkinter gives you a few special variable types that behave differently from normal Python strings. StringVar is one of them, and once I understood how it works, I found myself reaching for it whenever I needed a widget to display something that might change later. The key difference is that StringVar ties directly to a widget through its textvariable parameter, so updating the variable automatically updates what the user sees. I will walk through how to create, set, get, and watch these variables with real examples.

Most guides throw a dozen code snippets at you without explaining why you would use StringVar over a plain Python variable. I think the trace callback feature is the real reason it exists. It lets you react whenever the variable changes, which is how you build things like real-time validation or dynamic labels. Here is everything you need to know to start using it.

TLDR

• StringVar holds a string value and can be linked to a widget so the display updates automatically when the variable changes.
• Create it with tk.StringVar(master, value), set it with .set(), and read it with .get().
• Pass a StringVar to the textvariable parameter of any widget that supports it, like Label or Entry.
• Use .trace(mode, callback) with mode 'w' to run a function whenever the variable is modified.

What is StringVar?

Normal Python strings are just text. When you assign a new string to a variable, nothing in your GUI updates unless you manually change the widget displaying that text. StringVar solves this by acting as a bridge between a Python string and a Tkinter widget. You create a StringVar, link it to a widget via the textvariable parameter, and any call to .set() immediately reflects in the UI. The widget stays in sync without you writing extra update logic.

You can create a StringVar without arguments, or pass in a master window and an initial value. If you skip the master, Tkinter defaults to the root window. Here is the minimal version:

import tkinter as tk

root = tk.Tk()
my_var = tk.StringVar()  # empty string by default

Defining a StringVar with Parameters

The StringVar constructor accepts a few arguments that control its initial state and name:

• master: the window the variable belongs to. If you omit it, Tkinter uses the root window.
• value: the initial string value. Defaults to an empty string.
• name: a name for the variable. Tkinter generates one like PY_VAR1 if you leave it blank.

Here is a complete example showing all three parameters:

import tkinter as tk

root = tk.Tk()
root.geometry("200x100")

# Set an initial value and give it a name
greeting = tk.StringVar(root, "Hello!", "greeting_var")

label = tk.Label(root, textvariable=greeting, height=4)
label.pack()

root.mainloop()

Setting and Getting Values

There are two ways to set the value of a StringVar. The first is to pass it through the constructor, which I showed above. The second is to use the .set() method after creation:

name = tk.StringVar(root)
name.set("Alice")
print(name.get())  # Alice

The .get() method retrieves the current value as a plain Python string. You can call it any time you need the value in your code, whether or not the variable is linked to a widget.

Linking StringVar to Entry Widgets

One of the most common patterns is connecting a StringVar to an Entry widget. Whatever the user types into the entry field gets stored in the variable automatically, and any code that reads the variable sees the latest input without you having to poll the widget:

import tkinter as tk

def show_input():
    print(entry_var.get())

root = tk.Tk()
root.geometry("300x100")

entry_var = tk.StringVar()

entry = tk.Entry(root, textvariable=entry_var, width=30)
entry.pack(pady=10)

btn = tk.Button(root, text="Print value", command=show_input)
btn.pack()

root.mainloop()

Run this and type something into the entry field. When you click the button, it prints exactly what is currently in the field. No extra polling or event handling needed.

Watching Changes with trace()

The feature that makes StringVar genuinely useful is the trace() method. It lets you register a callback that fires whenever the variable is read, written, or deleted. You specify the mode as a string: 'w' for write, 'r' for read, 'u' for unset. Most of the time you want 'w' so your callback runs whenever the value changes.

import tkinter as tk

def on_name_change(*args):
    current = name_var.get()
    result_label.config(text=f"Hello, {current}" if current else "Enter your name")

root = tk.Tk()
root.geometry("300x120")
root.title("Greeting App")

name_var = tk.StringVar()
name_var.trace("w", on_name_change)

tk.Label(root, text="Name:").grid(row=0, column=0, padx=5, pady=5)
tk.Entry(root, textvariable=name_var).grid(row=0, column=1, padx=5, pady=5)
result_label = tk.Label(root, text="Enter your name", fg="gray")
result_label.grid(row=1, column=0, columnspan=2, pady=5)

root.mainloop()

The callback receives any extra arguments Tkinter passes in, which is why I used *args. The trace callback fires synchronously every time the variable changes, whether that happens through user input in an Entry widget or through an explicit call to .set() in your code.

FAQ

Q: Can I use StringVar with widgets other than Entry and Label?

A: Any widget that has a textvariable parameter works with StringVar. That includes Button, Checkbutton, Radiobutton, and Text (though Text is more complex). For widgets without a textvariable parameter, you update the display manually using .config(text=...).

Q: Should I use a plain Python variable instead of StringVar?

A: Use a plain Python variable when you never link it to a widget and when you do not need to react to changes. Use StringVar when you need two-way binding between a widget and a variable, or when you want trace callbacks to fire on changes. For simple cases where you set a label once and never update it, a plain variable is less overhead.

Q: What happens if I pass a StringVar to two widgets?

A: Both widgets display the same value, and both update whenever the variable changes. This can be useful for things like a header label and a status bar that always show the same message.

Q: Can I store non-string values in a StringVar?

A: You can pass an integer or float and Tkinter converts it to a string automatically. However, .get() always returns a string, so for numeric work you need to convert back with int() or float(). If you find yourself doing that a lot, consider using IntVar or DoubleVar instead.