os.listdir() lists data files but the corresponding assertion fails

Question

I have the following code which throws an assertion error. os.listdir() lists my data files but there is still an assertion error.

import os
PATH_TO_FOLDER = 'LOCAL PATH TO MY DATA'
assert 'data' in os.listdir(PATH_TO_FOLDER)
import sys
sys.path.append('..')

Why do you want to `assert 'data' in os.listdir(PATH_TO_FOLDER)`? Is it intended? If so, the problem may simply be that `'data'` is not a directory in your `PATH_TO_FOLDER`. — Anakhand, Jan 29 '19 at 11:42
What is the output of ``print('data' in os.listdir(PATH_TO_FOLDER))``? — DocDriven, Jan 29 '19 at 11:44
Please specify the dirs and files as well. I want to see how are you using paths. — CristiFati, Jan 29 '19 at 11:45
@Anakhand I wish to know why the assertion is failing, I have updated my assert statement to check for the folder name in my path. I guess its case sensitive — kuldeep kaur, Jan 30 '19 at 05:17

score 0 · Answer 1 · answered Jan 29 '19 at 11:44

0

The assertion error originates from the line

assert 'data' in os.listdir(PATH_TO_FOLDER)

If that line is intentional, the assertion fails simply because there exists no directory or file named 'data' in your PATH_TO_FOLDER directory.

answered Jan 29 '19 at 11:44

Anakhand

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I have fixed this but the assertion is still failing. The Path_To_Folder is 'D:\LUNA16\data\subset0' – kuldeep kaur Jan 30 '19 at 05:24
@kuldeepkaur So you checked the directory `'D:\LUNA16\data\subset0\data'` exists? If so, is it still giving an `AssertionError`? Or is the `'data'` directory you want to detect `'D:\LUNA16\data'`? – Anakhand Jan 30 '19 at 19:09
I checked that the directory exists. – kuldeep kaur Jan 31 '19 at 06:50
@kuldeepkaur Try to print out `os.listdir('D:\LUNA16\data\subset0')`. What is its complete output? – Anakhand Jan 31 '19 at 11:54

score 0 · Accepted Answer · answered Jan 30 '19 at 08:27

I was asking you to what the statement 'data' in os.listdir(PATH_TO_FOLDER) evaluates to. This returned False.

Knowing this I can tell you, assert works as intended. Assertions are Boolean expressions, depending on whether your statement 'data' in os.listdir(PATH_TO_FOLDER) is True or False. If it is True, then nothing happens and your code skips to the next line. If False, it raises an AssertionError. Assertions are meant to check if certain prerequisites are met.

Coming back to your issue: the error will stop from occuring if you make sure that your path is correct and you have a folder called data there. Also note that os.listdir() does not check for subfolders recursively.

It turns out I put the folder name in the path itself and was trying to look for a folder named 'data' inside the specified path. Thanks everyone for their time. Appreciate the help. — kuldeep kaur, Jan 31 '19 at 17:09

os.listdir() lists data files but the corresponding assertion fails

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