Python merge dicts without overwriting inner values

update.py

def update_key(key, value, d: dict):
    if key not in d:
        d[key] = value
    else:
        if isinstance(value, dict):
            for k, v in value.items():
                update_key(k, v, d[key])
        else:
            raise RuntimeError('Trying to overwrite existing value')


```
my_dict = {}
update_key('name', 'ron', my_dict)
print(my_dict)
{'name': 'ron'}
update_key('location', {'country': 'Israel'}, my_dict)
print(my_dict)
{'name': 'ron', 'location': {'country': 'Israel'}}
update_key('location', {'city': 'aaa', 'street': 'bbb'}, my_dict)
print(my_dict)
{'name': 'ron', 'location': {'country': 'Israel', 'city': 'aaa', 'street': 'bbb'}}
```