Python starmap got multiple values for argument

Question

I hava a multiprocess program whcich using starmap. But when I run it, a TypeError occured. While normally when I run it in map.

def process_single_image(img_path, target_dir="", func=None, severity=1):
    print(target_dir)
    ...

pool.starmap(
    partial(
        process_single_image,
        target_dir=target_dir,
        func=iaa.imgcorruptlike.apply_shot_noise,
        severity=4,
    ),
    img_paths,
)

I don't know why I got this error. I think it should run normally as pool.map(....). Here is the traceback.

Sure. I just add the screenshot of traceback in original post. — Whisht, Jul 18 '22 at 09:10
I conjecture that whether `starmap()` pass throug 2 arguments at least? — Whisht, Jul 18 '22 at 09:12
What does `img_paths` look like? It has to be an iterable of iterables. Also, post the traceback in text form rather than in an image. — Charchit Agarwal, Jul 18 '22 at 09:29
It's a list. you can use any string list for test. such as img_path =['abc','ab',..] — Whisht, Jul 18 '22 at 09:30

score 0 · Accepted Answer · answered Jul 18 '22 at 09:36

The arguments you pass to .starmap are unpacked to the target function. Therefore, the arguments must be an iterable of iterables (even if the argument length the target function accepts is one).

Therefore, if the argument length is one, then explicitly convert each element of img_path into a tuple before passing it to starmap:

img_path = [(arg,) for arg in img_path]

Python starmap got multiple values for argument

1 Answers1