Got some "Extra data" error from ffmpeg.probe :(

Hi! I've found this code:

input_file = file.webm
args = {"v": "error",
        "select_streams": "v:0",
        "count_packets": None,
        "show_entries": "stream=nb_read_packets",
        "of": "csv=p=0"
        }

pb = (ffmpeg
          .probe(input_file , **args)
          )

when I run the code I got this error: json.decoder.JSONDecodeError: Extra data: line 1 column 2 (char 1)

If I delete the : "of": "csv=p=0" , it works, I've also tried: "of":"default=noprint_wrappers=1:nokey=1", same problem. I think is the amount of "=" ? I hope I can get some advice. Thanks!