The json.decoder.JSONDecodeError error of Pyhton cannot be solved.

1. After the emergence of json.decoder.JSONDecodeError, Baidu in the process of practicing using JSON, I still can"t find a solution. I hope there is a great god who can help me to answer it.
2. The code is as follows:
import json

def get_stored_num ():

try:
    with open("num.json") as f_obj:
        num=json.load(f_obj)
except FileNotFoundError:
    return None
else:
    return num

def get_new_num ():

num=input("tell me your favourite num: ")
with open("num.json","w") as f_obj:
    json.dump(num,f_obj)
return num
    

def num_print ():

num=get_stored_num()
if num:
    print("i know your favroite num is: "+ num)
else:
    num=get_new_num()
    print("your favouite num is: "+num)

num_print ()

Mar.07,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e53e30-4525c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e53e30-4525c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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