[Python] pyyaml resolver: 'type' object is not iterable

I am trying to resolve environment variables in yaml config

For example, I want to convert

car:
name: ${CAR_NAME}
is_new: true


to

car:
name: BMW
is_new: true


My code

# base_model.py

import yaml
import os
import re

from pydantic import BaseModel
from typing import Union
from pathlib import Path


env_pattern = re.compile(r".*?\${(.*?)}.*?")
def env_constructor(loader, node):
value = loader.construct_scalar(node)
for group in env_pattern.findall(value):
value = value.replace(f"${{{group}}}", os.environ.get(group))
return value

yaml.add_implicit_resolver("!pathex", env_pattern, yaml.SafeLoader)
yaml.add_constructor("!pathex", env_constructor, yaml.SafeLoader)


class YamlModel(BaseModel):
@classmethod
def from_yaml(cls, yaml_file_path: Union[str, Path]) -> "YamlModel":
yaml_file = Path(yaml_file_path)
with open(yaml_file, "r") as f:
file_content = yaml.safe_load(f)

return cls.parse_obj(file_content)


My test

import pytest
import pydantic

from src.example_model import Config


def test_config_positive():
config = Config.from_yaml("tests/config_positive.yaml")
assert config.owner.name == "John Doe"
assert config.owner.age == 30
assert config.car.name == "BMW"


I have an error:

tests/test_example_model.py:4: in <module>
from src.example_model import Config
src/example_model.py:1: in <module>
from src.base_model import YamlModel
src/base_model.py:17: in <module>
yaml.add_implicit_resolver("!pathex", env_pattern, yaml.SafeLoader)
venv/lib/python3.11/site-packages/yaml/__init__.py:280: in add_implicit_resolver
loader.Loader.add_implicit_resolver(tag, regexp, first)
venv/lib/python3.11/site-packages/yaml/resolver.py:34: in add_implicit_resolver
for ch in first:
E TypeError: 'type' object is not iterable



Full code https://github.com/mascaiTemplates/yaml_config_validator_template

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