Is there a python equivalent to Laravel 4?

You can look at the framework I'm currently building, namely glim. There exists inspiration from play framework & laravel in it. You can get more information from the docs page.

It also has an extension system where developers can integrate to it. You can look at the extensions I have built;

Python also has a web framework called Masonite which is a lot like Laravel. Heavily inspired by Laravel and a lot of Laravel developers can pick it up really easily.

Also has an ORM called Masonite ORM which is heavily inspired by eloquent

Yes. Pyramid is what you are looking for. It's written from the ground up to be based in common Python libraries and components, and you can swap out pieces for other pieces as you wish. Python as a language is geared for TDD, and Pyramid takes advantage of that. You can push your own libraries, if they are abstract enough, out to PyPi for yourself, if you wish, but you can of course just keep them within your own projects too.

There are other Python frameworks, but if you're looking for modular and extensible, without a whole lot of framework interference in your working style preference, Pyramid is the way to go.

P.S. this question is better suited for programmers.stackexchange.com.