When comparing Tkinter vs Flutter, the Slant community recommends Flutter for most people. In the question“What are the best cross-platform GUI toolkits?” Flutter is ranked 15th while Tkinter is ranked 20th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
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
Pro Open source
Pro Great developer tools debug/hotreload/analyser
Pro Based on Dart language
Dart is a Java like language, easy to learn and startup fast for millions of Java developers.
Pro A single codebase for iOS AND Android
Pro Fast
The developer's goal is to allow people to make apps running at 120 FPS.
Cons
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.
Con Still in development
According to the website, Flutter is still in its early stages of development.
Con Based on Dart language
Dart is a Java like language, easy to learn and startup fast for millions of Java developers. BUT if you have to learn it ... it's a con.
Con Dart is unpopular and never gained serious community traction like Kotlin or Java
Con Does not support 32-bit iOS devices
If you plan on targeting iPhone 5, 5C or earlier, you can forget about Flutter.