Unity's primary development language is C#. I am not aware of any way to add a new scripting language to Unity which works just like a native one.
But you can call Python from C# using IronPython. So you could implement a stub for each MonoBehaviour in C# which doesn't do more than call a Python script to implement the actual logic.
The end result might be that for many classes, the boilerplate C# code to call the Python implementation will be more code than the Python implementation itself. Also, there will be performance overhead for the switching between C# and Python, so your game won't be as fast as it would be when developed in pure C#.
Or you could just learn C#. The hardest part when learning a new programming language is usually to learn how to use all the libraries and APIs you need to do something productive with them. And you will have to learn the Unity scripting API anyway, no matter which programming language you use to call it.