Flatten a dictonary , nested dictionary into plain dictonary

flatten_dict.py

def flatten(data):
    flatten_dict = {}
    def flat(data_, key, pkey=''):
        if isinstance(data_, dict):
            if data_ == dict():
                flatten_dict[f"{pkey}"] = data_
            for key, value in data_.items():
                key_fmt = [pkey, key]
                if pkey == '':
                    key_fmt = [key]
                flat(value, key, '.'.join(key_fmt))
            return data_
        elif isinstance(data_, list):
            if data_ == list():
                flatten_dict[f"{pkey}"] = data_
            temp = []
            for i, item in enumerate(data_):
                key_fmt = [pkey, str(i)]
                if pkey == '':
                    key_fmt = [str(i)]
                temp.append(flat(item, key, '.'.join(key_fmt)))
            return temp
        elif data_ is None:
            return None
        flatten_dict[f"{pkey}"] = data_
        return data_
    flat(data, '')
    return flatten_dict

flatten({'hello': 'world', 'nice': ['here', {'car': 'masarati', 'mo': 'dl'}], 'gabagool': {'category': ['food'], 'taste': 'good'}})