Convert dict to flat dict

flatten.py

import collections

def flatten(d: dict, parent_key='', sep='__', flat_lists=False) -> dict:
    """
    >>> flatten({'name': 'Ivan', 'mother': {'name': 'Alisha'}})                                                                                                           
    {'name': 'Ivan', 'mother__name': 'Alisha'}
    
    >>> flatten({'name': 'Ivan', 'brothers': [{'name': 'Jack'}]}, flat_lists=True)                                                                                        
    {'name': 'Ivan', 'brothers_0__name': 'Jack'}

    >>> flatten({'name': 'Ivan', 'brothers': ['Jack', 'Harry']}, flat_lists=True)                                                                                         
    {'name': 'Ivan', 'brothers_0': 'Jack', 'brothers_1': 'Harry'}

    >>> flatten({'name': 'Ivan', 'brothers': ['Jack', 'Harry']}, flat_lists=False)
    {'name': 'Ivan', 'brothers': ['Jack', 'Harry']}
    """
    if not isinstance(d, dict):
        if flat_lists:
            return {parent_key: d}
        return d

    res = {}
    for k, v in d.items():
        new_key = parent_key + sep + k if parent_key else k
        if isinstance(v, collections.MutableMapping):
            res.update(flatten(v, new_key))
        elif isinstance(v, list):
            if flat_lists:
                for i, obj in enumerate(v):
                    res.update(
                            flatten(obj, '{}_{}'.format(new_key, i), sep=sep, flat_lists=flat_lists))
            else:
                res[new_key] = [flatten(obj) for obj in v]
        else:
            res[new_key] = v
    return res