Python: FileNotFoundError not caught by try-except block

Question

recently i started learning Python and encountered a problem i can`t find an answer to. Idea of the program is to ask for username, load a dictionary from JSON file, and if the name is in the dictionary - print the users favourite number.

The code, that loads the JSON file looks like this:

import json

fav_numbers = {}
filename = 'numbers.JSON'

name = input('Hi, what`s your name? ')
try:
    with open(filename) as f_obj:
        fav_numbers = json.load(f_obj)
except FileNotFoundError:
    pass

if name in fav_numbers.keys():    

    print('Hi {}, your fav number is {}, right?'.format(name, fav_numbers[name]))

else:
    number = input('Hi {}, what`s your favourte number? '.format(name))
    fav_numbers[name] = number

    with open(filename, 'w') as f_obj:
        json.dump(fav_numbers, filename)

Still, as i try to run it, it crashes, telling me:

Exception has occurred: FileNotFoundError
[Errno 2] No such file or directory: 'numbers.JSON'
  File "/home/niedzwiedx/Dokumenty/Python/ulubionejson.py", line 22, in <module>
    with open(filename) as f_obj:

What i`m doing wrong to catch the exception? (Already tried changing the FileNotFoundError to OSError or IOError)

The error probably comes from somewhere else in your code. Can you provide more code and the full traceback for the error ? — Valentin M., Jan 23 '20 at 10:52
Your edited code should not match the error provided. If the file does not exists, it should fail on line 13 with a ``KeyError`` when accessing ``if fav_numbers[name]: `` As for your edited question: line 22 is not wrapped in a ``try..except`` block, only the lines 8 and 9 are. — Mike Scotty, Jan 23 '20 at 11:12
Your traceback still does not match the code you provide : `with open(filename) as f_obj:` in you traceback is actually `with open(filename, 'w') as f_obj:` in your code. Are you sure that you run the same file that you are editing ? — Valentin M., Jan 23 '20 at 13:32

Valentin M. · Answer 1 · 2020-01-23T13:52:30.680

The error comes from you last line, outside of your try/except

with open(filename, 'w') as f_obj:
        json.dump(fav_numbers, filename)

filename is a string, not a file.

You have to use

with open(filename, 'w') as f_obj:
        json.dump(fav_numbers, f_obj)

For additional safety, you can surround this part with try/except too

try:
    with open(filename, 'w') as f_obj:
        json.dump(fav_numbers, f_obj)
except (FileNotFoundError, PremissionError):
    print("Impossible to create JSON file to save data")

Python: FileNotFoundError not caught by try-except block

1 Answers1