[Python] Reading and writing dictionary

So I thought about writing a program that takes a URL address and shortens it. I want the program to be able to write every new URL and store it in a file and generate a new short one and if the user tries to shorten the same address it'll pull out of the dictionary the result the user got last time he put this address. I set the KEY to the full URL and the VALUE to the short version. I tried to do it but when I try to read it gives me this error:

(key, val) = line.split()
ValueError: too many values to unpack (expected 2)


import random
import string
import json

#Default items
dict_url = {
'instagramcom/rois..../': "https:/roi.sl/2Ly8PzD",
'instagramcom/....../': "https://roi.sl/2YqJa12"
}
#Updated_dict will be the dict i'll be using to input and output data
updated_dict = {}
updated_dict.update(dict_url)
#writing the default items from dict_url so updated_dict will have something
with open('UrlDB.txt', 'w') as file_write:
file_write.write(str(updated_dict))
updated_dict.update(dict_url)

#trying to read the file
with open('UrlDB.txt', 'r') as file_read:
for line in file_read:
(key, val) = line.split()
updated_dict[key] = val



while True:
new_url = ""
exs_url = ""
base_form = "https:/roi.sl/"
user_input = input("Please Enter the URL: ")
if user_input in dict_url:
exs_url = dict_url.get(user_input)
print(exs_url)

break
else:
rnd_comb = (random.choices(string.ascii_uppercase + string.ascii_lowercase + string.digits, k=6))
rnd_comb_str = ''.join(rnd_comb)
new_url = base_form + rnd_comb_str
new_item = {
user_input: (3, new_url)
}
file_write.write(str(new_item))
dict_url.update(new_item)
print(new_url)
break

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