This is for traversing arbitrary values, maybe trees, and applying a transformation to each node.

visitor_traverser.py

import inspect
from typing import (Callable, Optional, Any)
import unittest

def build_traverser(*, visitor: Callable[[Any, Optional[str]], Any]) -> Callable[[Any], Any]:
  func = visitor
#   would prefer to insert a map here instead positional args. Don't have time for the moment on applying this here.
  if len(inspect.signature(func).parameters.values()) < 2:
    def visitor_wrapper(val, _key=None):
      return visitor(val)
    func = visitor_wrapper

  def traverse(val):
    if isinstance(val, dict):
      collector = {}
      for prop in val:
        collector[prop] = traverse(func(val[prop], prop))
      return collector
    if isinstance(val, list) and len(val) > 0:
      items = []
      for item in val:
        items.append(traverse(item))
      return items
    return func(val)

  return traverse
  


class Test(unittest.TestCase):
  def test_objects(self):
    def email_visitor(node, key=None):
      if key == 'email':
        return {'active':1}
      return node

    email_traverser = build_traverser(visitor=email_visitor)

    obj = {'key': 1, 'email': {}}
    result = email_traverser(obj)
    expectation = {'key': 1, 'email': {'active': 1}}
    self.assertEqual(result, expectation)

  def test_lists(self):
    def email_visitor(node, key=None):
      if key == 'email':
        return {'active':1}
      return node

    email_traverser = build_traverser(visitor=email_visitor)

    arg = [{'email': {}}]
    result = email_traverser(arg)
    expectation = [{'email': {'active': 1}}]
    self.assertEqual(result, expectation)
  
  def test_primitives(self):
    def primitive_visitor(node):
      if node == 1:
        return 'ONE'
      if node == 'a':
        return 'A'
      return node

    primitive_traverse = build_traverser(visitor=primitive_visitor)
    tables = [
      (1, 'ONE'),
      ('a', 'A')
    ]
    for arg, expectation in tables:
      result = primitive_traverse(arg)
      self.assertEqual(result, expectation)

if __name__ == "__main__":
  unittest.main()