When comparing pyglet vs Duality, the Slant community recommends Duality for most people. In the question“What are the best 2D game engines?” Duality is ranked 30th while pyglet is ranked 43rd. The most important reason people chose Duality is:
The full source code is available on GitHub, where the framework is actively developed. All of the editor, core and plugin code is written in C#.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro 3D support
Since pyglet is so tightly woven with OpenGL it allows the support of drawing in 3D.
Pro Cross-platform
Works with Windows, Linux, and OS X.
Pro Written in pure Python
A small advantage, but being a core Python developer, it may be the best to stick to the roots and develop with pyglet as it is able to compile using other Python interpreters.

Pro Open source
The full source code is available on GitHub, where the framework is actively developed. All of the editor, core and plugin code is written in C#.

Pro Great editor
Duality includes a powerful visual editing system that can be used for previewing, integrating, editing and testing game content.

Pro Live reload of code and assets

Pro Very extensible
Because both Core and Editor are completely plugin-based, Duality not only incorporates a clean and modular design, but is also very extensible - even if it wasn't Open Source. In fact, most of the standard editing capabilities comes in form of Editor plugins.

Pro Built-in physics and lighting

Pro Friendly to version control systems
It can be configured to serialize all data in a text-based format, which has been structurally optimized for version control systems.

Pro Used in commercial projects
It has been used in a production environment without burning the place to the ground. Supposedly artist-proof editor workflow with an API for tailoring the system to fit your team.
Cons
Con Small community/popularity
There is a decent amount of documentation and API to go along with pyglet, but in terms of community support there seems to be very little.
Con Visual Studio required
To have possibility for scripting you have to download entire Visual Studio and spend 10 GB of free space
Con Requires windows for development
