Just to answer the OP directly.
NO, you cannot make a commercial, 3D FPS/RPG/SHOOTER/etc, IN Python.
But, you CAN totally make it WITH Python.
What does that mean. It means that you can program the game in python, and use modules that calls on lower language (like C, or even C++) to run the game for you.
Panda3D is one example of this.
-Exo

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