pdfconverter: Use file path for image conversion

[manoedinata]

Instead of appending the image content, we could instead use the file path for img2pdf. This reduces huge memory consumption during image conversion (tested in 1GB machine, process getting killed if using image content).

File path usage is also documented in the library homepage in PyPI [1].

[1] https://pypi.org/project/img2pdf/

[manoedinata]

Oh, thanks for making this script! It really helps me to download eBook from Fliphtml5 easily :)

[manoedinata]

Oh wait! The PDF conversion is failing on Windows system. Please don't merge it just yet!

[marcorentap]

Yeah using the paths would be better, I didn't realize that when I made this tool...

It's not working on Windows probably because windows uses \ instead of / as the path separator. Usually we use os.path.join() which handles the differences between OSes. But since Python 3.4, pathlib was introduced. I find it much more convenient to use.

I think we should use it to create the filepath instead of using the basic string "{0}/{1}.jpg".format(folderName, num)

[marcorentap]

Also, since Python 3.6, there's f-strings. I think they are much more readable than str.format():

with open(f"{folderName}.pdf", "wb") as file:
    ...

# Instead of this
with open("{0}.pdf".format(folderName), "wb") as file:
    ...

It would be a good idea to start using this whenever we need formatted strings