When comparing nuklear vs Tkinter, the Slant community recommends nuklear for most people. In the question“What are the best cross-platform GUI toolkits?” nuklear is ranked 7th while Tkinter is ranked 20th.
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Pros

Pro A single-header ANSI C gui library
Pro No dependencies (not even the standard library if not wanted)
Pro MIT/Public Domain License
Pro Focus on portability, efficiency and simplicity
Pro Small codebase (~18kLOC)
Pro Bindings for popular languages
Bindings for languages like C#, Java, Python, Go, Nim, Lua and Rust.
Pro Fully skinnable and customizable
Pro Customizable library modules (you can compile and use only what you need)
Pro Free for commercial use
Pro Included in the standard Python library
You probably already have it, since it's included in the standard Python distributions.
Pro Easy to learn and get productive with
TkInter is a small library with a gentle learning curve compared to what’s out there. It has a straightforward API and is often the go-to choice for building quick GUIs for Python scripts.
Pro Building executables is less complicated
Compared to other GUI libraries, building executables for TkInter applications are simpler because TkInter is included in Python and has no other dependencies. This results in less complicated packaging requirements and smaller binary size.
Pro Fast
Cons
Con Very limited documentation
Con No input or output implementation provided
User must connect with OS or other libraries to get input or display output on any platform.
Con No advanced widgets
TkInter does not come with advanced widgets out of the box (e.g. date picker).
Con Not good looking
You need a lot of code to make it look good.
Con No reliable UI builder available
There is no tool in the same league as Qt Designer (PyQt) for TkInter.
