Question

I’m trying to call an ImageMagick command from Python 2.7 using subprocess.call. My problem is that the argument parser in subprocess puts a double quotation mark around every argument, and ImageMagick seems to have a problem with quotes around non-file arguments.

What I’d like is something like this

"imagemagick.exe" "im1.png" "im2.png" -alpha off ( ... ) -composite "im3.png"

So far I couldn’t find a way to do it with subprocess, other than manually constructing the string with ugly + " " + elements and calling it with shell=True.

Here is my code:

args = [    imagemagick,
            filename + "_b.bmp",
            filename + "_w.bmp",
            "-alpha off ( -clone 0,1 -compose difference -composite -negate ) ( -clone 0,2 +swap -compose divide -composite ) -delete 0,1 +swap -compose Copy_Opacity -composite",
            filename + ".png" ]   

subprocess.call( args )

Is there any way to call the correct command without double quotes using subprocess?

Update: inserted the full command line. I’d like to keep that part together, not as “alpha”, “-off”, … one by one.

Answer 1

When calling external programs with subprocess, every argument must be a different element of args. So try:

args = [    imagemagick,
            filename + "_b.bmp",
            filename + "_w.bmp",
            "-alpha", "off", "( ... )", "-composite",
            filename + ".png" ]

I’m not sure what the ( ... ) represents, but if you put unquoted spaces in there on the command line, they should be separate elements in args too.