util for seeing if dictionary has path

dict_has_path.py

def dict_has_path(d, path):
  if not isinstance(d, dict):
    return None, 'dict_has_path expected type dict for d parameter. called with %s' % d.__class__.__name__
  if not isinstance(path, str):
    return None, 'dict_has_path expected type str for path parameter.  called with %s' % path.__class__.__name__
  if path in d:
    return True, None
  if '.' not in path:
    return False, None
  sub_paths = path.split('.')
  first, rest = sub_paths[0], sub_paths[1:]
  if first not in path:
    return False, None
  next_val = d.get(first)
  if not isinstance(next_val, dict):
    return False, None
  return dict_has_path(next_val, '.'.join(rest))

class DictHasPathTestsTest(unittest.TestCase):
  def test_called_with_non_dict_error(self):
    has_path, err = dict_has_path(None, 'adsf')
    self.assertEqual(None, has_path)
    self.assertRegexpMatches(err, r'expected type dict')

  def test_called_with_non_string_path(self):
    has_path, err = dict_has_path({}, None)
    self.assertEqual(None, has_path)
    self.assertRegexpMatches(err, r'expected type str')

  def test_shallow_true(self):
    has_path, err = dict_has_path({'age': 1}, 'age')
    self.assertEqual(has_path, True)
    self.assertEqual(err, None)

  def test_shallow_false(self):
    has_path, err = dict_has_path({'age': 1}, 'name')
    self.assertEqual(has_path, False)
    self.assertEqual(err, None)

  def test_nested_true(self):
    has_path, err = dict_has_path({'name': {'first': 'bo'}}, 'name.first')
    self.assertEqual(has_path, True)
    self.assertEqual(err, None)

  def test_nested_false(self):
    has_path, err = dict_has_path({'name': {'first': 'bo'}}, 'name.last')
    self.assertEqual(has_path, False)
    self.assertEqual(err, None)