How to use dask for function with no return ? (image processing)

Question

I have a function crop_images_circle(file_dir,kmeans_dir,folders_dir,filename). that does not return any thing. Trying to use dask to parallalise the computation.

Implementation without dask for some 100 odd files:

for filename in os.listdir(file_dir):
    crop_images_circle(file_dir,kmeans_dir,folders_dir,filename)

Execution time in seconds: 53.58223843574524

Implementation with dask :

# Version 1
for filename in os.listdir(file_dir):
    x = delayed(crop_images_circle)(file_dir,kmeans_dir,folders_dir,filename)
    x.compute()

Execution time in seconds: 46.36917209625244

# Version 2
for filename in os.listdir(file_dir):
    x = delayed(crop_images_circle)(file_dir,kmeans_dir,folders_dir,filename)

x.compute()

Version 2 of dask just process one Image. Not sure why. Documentation does mention similar use, TIme required is not that significantly different. Is there a improvement using a dask ? Or I am messing up the syntax?

Answer 1

This is from dask best practices. might answer the quesion above

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Don’t rely on side effects

Delayed functions only do something if they are computed. You will always need to pass the output to something that eventually calls compute.