Python ast module relies on _ast.py to define all specific AST nodes. By inspecting the file, it appears it is a generated file (as of 3.8):
# encoding: utf-8
# module _ast
# from (built-in)
# by generator 1.147
I would like to inspect the source code of the generator creating this file in CPython code, but I can't find it. I have tried searching the source for _ast, 1.147, generator *. ast and other searches with no success.