Python转换PDF

Question

I have the following code to create multiple jpgs from a single multi-page PDF. However I get the following error: wand.exceptions.BlobError: unable to open image '{uuid}.jpg': No such file or directory @ error/blob.c/OpenBlob/2841 but the image has been created. I initially thought it may be a race condition so I put in a time.sleep() but that didn't work either so I don't believe that's it. Has anyone seen this before?

def split_pdf(pdf_obj, step_functions_client, task_token):
    print(time.time())

    read_pdf = PyPDF2.PdfFileReader(pdf_obj)
    images = []

    for page_num in range(read_pdf.numPages):
        output = PyPDF2.PdfFileWriter()
        output.addPage(read_pdf.getPage(page_num))

        generateduuid = str(uuid.uuid4())
        filename = generateduuid + ".pdf"
        outputfilename = generateduuid + ".jpg"
        with open(filename, "wb") as out_pdf:
            output.write(out_pdf) # write to local instead

        image = {"page": str(page_num + 1)}  # Start at 1 rather than 0

        create_image_process = subprocess.Popen(["gs", "-o " + outputfilename, "-sDEVICE=jpeg", "-r300", "-dJPEGQ=100", filename], stdout=subprocess.PIPE)
        create_image_process.wait()

        time.sleep(10)
        with(Image(filename=outputfilename)) as img:
            image["image_data"] = img.make_blob('jpeg')
            image["height"] = img.height
            image["width"] = img.width
            images.append(image)

            if hasattr(step_functions_client, 'send_task_heartbeat'):
                step_functions_client.send_task_heartbeat(taskToken=task_token)

    return images

Answer 1

It looks like you aren't passing in a value when you try to open the PDF in the first place - hence the error you are receiving.

Make sure you format the string with the full file path as well, eg f'/path/to/file/{uuid}.jpg' or '/path/to/file/{}.jpg'.format(uuid)

Answer 2

I don't really understand why your using PyPDF2, GhostScript, and wand. You not parsing/manipulating any PostScript, and Wand sits on top of ImageMagick which sits on top of ghostscript. You might be able to reduce the function down to one PDF utility.

def split_pdf(pdf_obj, step_functions_client, task_token):
    images = []
    with Image(file=pdf_obj, resolution=300) as document:
        for index, page in enumerate(document.sequence):
            image = {
                "page": index + 1,
                "height": page.height,
                "width": page.width,
            }
            with Image(page) as frame:
                image["image_data"] = frame.make_blob("JPEG")
            images.append(image)
            if hasattr(step_functions_client, 'send_task_heartbeat'):
                step_functions_client.send_task_heartbeat(taskToken=task_token)
    return images

I initially thought it may be a race condition so I put in a time.sleep() but that didn't work either so I don't believe that's it. Has anyone seen this before?

The example code doesn't have any error handling. PDFs can be generated by many software vendors, and a lot of them do a sloppy job. It's more than possible that PyPDF or Ghostscript failed, and you never got a chance to handle this.

For example, when I use Ghostscript for PDFs generated by a random website, I often see the following message on stderr ...

ignoring zlib error: incorrect data check

... which results in incomplete documents, or blank pages.

Another common example is that the system resources have been exhausted, and no additional memory can be allocated. This happens all the time with web servers, and the solution is usually to migrate the task over to a queue worker that can cleanly shutdown at the end of each task-completion.