How to create feature vector for AST vertices?

Question

Python

There is to_test.py code:

file = open(name_of_file, "a")
file.write(alpha_expression + "\n")
file.close()

I translated it into AST:

import ast
with open("for_test.py", "r") as source:
    tree = ast.parse(source.read())
print(ast.dump(tree))

how to create feature vectors for each vertex?