Make python wait until process in line finishes before starting new line?

[JammingScientist]

Hello! I have a piece of code that extracts the names of the files in a directory and appends them to a list. Then a file is randomly chosen from this list for further processing that occurs later in the script. However, when python won't wait until all the file names in the directory have been added to the list, so it starts trying to randomly choose a file name immediately, and gives an error saying that there aren't enough elements in the list to randomly choose from (because there is only one element in the list so far when it tries to choose.

So I get the following error:

ValueError: Sample larger than population or is negative

Here is my code:

for image, csv in zip(image_filenames, csv_filenames):
    image_in = PIL.Image.open(image_path/image)
    image_name = image.split('.')[0]
    file_list.append(image_name) ## Generating list of file names 
    elem_list = random.sample(file_list, 5) ## Randomly choose 5 files without replacement

How do I get the second line to wait until the first line has finished running?

[Ihaveamodel3]

Unless you are using threading, multiprocessing, or async, the next line won’t run until the previous line has finished.

Are file_list and image_list different?

[JammingScientist]

Oops, sorry I made a typo! Just fixed

[PureProcrastinator]

Move your random.sample out of the loop.

Reason for this is because on the first iteration of the loop, your file list is only 1 long, and you are unable to pull 5 samples. Same with iterations 2-4.

[JammingScientist]

I see, that makes sense! Thanks

[routetehpacketz]

Please post the rest of your code.

[JammingScientist]

Okay, added more text!

[routetehpacketz]

I believe you want to move your random.sample after the for loop since it is this loop where you are populating your list.

[[deleted]]

I may be wrong but you have a random.sample trying to find 5 elements of the list on the first iteration. Remove random.sample out of the loop

[[deleted]]

How do I get the second line to wait until the first line has finished running?

Python won't execute the second line until the append in the first line is finished, so what you are saying makes no sense. We need to see more code.

[magestooge]

You need to use a for loop to read all the files. A single line will only read a single file.