try except in a while loop - python

Question

Before explaining my question I share my code so it it easier to start directly from there.

import matplotlib.pylab as plt
import os

while True:
    try:
        img_name = input('Enter the image file name: ')
        img = plt.imread(os.path.join(work_dir, 'new_images_from_web\\', img_name + '.jpg'))
    except FileNotFoundError:
        print('Entered image name does not exist.')
        img_name = input('Please enter another image file name: ')
        img = plt.imread(os.path.join(work_dir, 'new_images_from_web\\', img_name + '.jpg'))

I would like the user to input the name of an image file, and whenever the file does not exist in the directory I want the user to input another file name instead of receiving an error message like the following:

FileNotFoundError: [Errno 2] No such file or directory:

In fact, with the code above, after the second mistaken input I receive an error message with exception FileNotFoundError, whereas I would like the loop to go on until an existing file name is given as input. What am I doing wrong in the while loop or in the rest of the code?

@SuperStew I don't think it's the loop, but the first time it works it is for the try: except: part — Ric S
– Ric S, Commented Jan 14, 2019 at 22:59

Patrick Artner · Accepted Answer · 2019-01-14 23:09:25Z

3

If a exception happens outside of try: except: it will crash your program. By asking a new input after the except: you are outside the capturing-"context": resulting in your program crashing.

Fix :

import matplotlib.pylab as plt
import os

while True:
    try:
        img_name = input('Enter the image file name: ')
        img = plt.imread(os.path.join(work_dir, 'new_images_from_web\\', img_name + '.jpg'))
        if img is None:
            print("Problem loading image")
        else:
            break  
    except FileNotFoundError:
        print('Entered image name does not exist.')

# or check img here if you allow a None image to "break" from above
if img:
    # do smth with img if not None

It is important to also check/handle img being None because imread() can return a None if problems occure with loading the image (file exists / but corrupted... or a .txt)

edited Jan 14, 2019 at 23:09

answered Jan 14, 2019 at 23:00

Patrick Artner

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Comments

Jundullah · Accepted Answer · 2019-01-14 23:31:01Z

0

This helps!

while Ture:
    try:
        img_name = input('Enter the image file name: ')
        img = plt.imread(os.path.join(work_dir, 'new_images_from_web\\', img_name + '.jpg'))
        if not img:
            print("Err")
        else:
            break
    except FileNotFoundError:
        print('Entered image name does not exist.')
    else:
        break

edited Jan 14, 2019 at 23:31

answered Jan 14, 2019 at 23:16

Jundullah

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