PyMongo: convertation BSON to Dict not working

my code here:

import os

import bson
from bson.codec_options import CodecOptions

bson_codec_options = CodecOptions(
    datetime_conversion='DATETIME_AUTO',
    tz_aware=True,
    unicode_decode_error_handler='ignore'
)
if __name__ == '__main__':
    current_dir = os.getcwd()
    bson_files = []

    for file in os.listdir(current_dir):
        current_item = os.path.join(current_dir, file)
        if os.path.isfile(current_item) and file.endswith(".bson"):
            bson_files.append(file)

    for file in bson_files:
        
        with open(os.path.join(current_dir, file), 'rb') as fcache:
            data = bson.decode(fcache.read(), codec_options=bson_codec_options)
            print(data)

I try to convert BSON to JSON. But I get error:

File "C:\PyProjects\zulip\.venv\Lib\site-packages\bson\__init__.py", line 1094, in decode
return cast("Union[dict[str, Any], _DocumentType]", _bson_to_dict(data, opts))
                                                    ^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'str' object cannot be interpreted as an integer

I hope anyone had already encountered such error, what did you do?