Why Should I Avoid Multiple Tk Instances in Tkinter?

Multiple Instances of Tk: A Cautionary Tale

In Tkinter, a popular GUI library for Python, creating multiple instances of the root (Tk) widget is generally discouraged for several reasons.

Multiple Tk Instances and Tcl Sandbox Isolation

Tkinter primarily manages an embedded Tcl interpreter with Tk libraries. Each created root window establishes a separate Tcl interpreter instance, forming an isolated sandbox. Within this sandbox, created elements like variables and widgets remain exclusive to that specific instance.

This poses potential issues. For example, a string variable created in one interpreter cannot be accessed in another. Similarly, widgets cannot have parent widgets from different interpreters, and images created in one interpreter are unusable in others.

Advantages of Single Tk Instance

Creating multiple instances of Tk can result in implementation hurdles. Most applications work effectively with a single Tk instance throughout their lifecycle. Using Toplevel widgets for additional windows overcomes this issue.

Second Example: Limited Improvement

The second code snippet in the question attempts to address Tk instance proliferation. Although it creates instances on-demand, the underlying issue remains. Sandboxes are still isolated, leading to potential problems with variables, widgets, and images across instances.

Best Practice: Single Tk, Multiple Toplevel

To mitigate these issues, it's recommended to establish a single, persistent Tk instance for your GUI application. Utilize Toplevel widgets to create subsequent windows within this primary Tk instance, respecting the intended design and structure of Tkinter and the underlying Tcl/Tk interpreter.

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