Show HN: I am building a new Python library to read/write PDF files

#1

Post by desgeeko » Thu, Nov 17, 2022, 10:38 PM UTC

Hi HN! This is my pet project, written from scratch because there is so much to discover and learn in the process. The focus is on simplicity and incremental updates. Progress is slow because I do not have much spare time to work on this, but I would love to hear some feedback. Regards

Show HN: I am building a new Python library to read/write PDF files
github.com

Re: Show HN: I am building a new Python library to read/write PDF files

#2

Post by password4321 » Fri, Nov 18, 2022, 12:25 AM UTC

Is there a list of open source PDF libraries for various languages?

And related: the best tools to generate PDFs from HTML.

Re: Show HN: I am building a new Python library to read/write PDF files

#3

Post by jonathansa » Fri, Nov 18, 2022, 12:26 AM UTC

Awesome work

Re: Show HN: I am building a new Python library to read/write PDF files

#4

Post by neilv » Fri, Nov 18, 2022, 12:27 AM UTC

Neat. Another use case for which you might want to think about a sample is extracting data from filled PDF forms. (That use case is why I once had to write a PDF parser.)

Since you read&write, maybe also a use case of programmatically filling some form fields in an editable PDF form. Such pre-filling some of the fields for a particular Web site user in a dynamically-modified PDF form they download. But the source PDF form can be hand-crafted and maintained separately, like people often want to do, not generated from scratch by your code.

Re: Show HN: I am building a new Python library to read/write PDF files

#5

Post by Spivak » Fri, Nov 18, 2022, 12:31 AM UTC

I wish you all the best! This space has a lot of stuff in it and they’re lacking in some aspect. And that’s not a admonishment, PDF is such a complicated format that there will never be a library that doesn’t come with asterisks — it’s just a matter of picking the thing you want your library to focus on and be good at and you can pretty easily be someone’s favorite lib.

Re: Show HN: I am building a new Python library to read/write PDF files

#6

Post by mdaniel » Fri, Nov 18, 2022, 12:32 AM UTC

I never knew about the J number suffix in python: https://docs.python.org/3/reference/lexical_analysis.html#im... which it would appear is used to represent references: https://github.com/desgeeko/pdfsyntax/blob/main/tests/test_p...

I wish you good luck, this file format has tripped up many, many a developer. It blew up on a pdf I had lying around:

    ValueError: could not convert string to float: b'5.0.0'


    104 0 obj > endobj

as it seems a string with nested parens jams up the parser

Re: Show HN: I am building a new Python library to read/write PDF files

#7

Post by mdaniel » Fri, Nov 18, 2022, 12:39 AM UTC

mdaniel wrote: post #6

I never knew about the J number suffix in python: https://docs.python.org/3/reference/lexical_analysis.html#im... which it would appear is used to represent references: https://github.com/desgeeko/pdfsyntax/blob/main/tests/test_p... I wish you good luck, this file format has tripped up many, many a developer. It blew up on a pdf I had lying around: ValueError: could not convert string to float: b'5.0.0' 104 0 obj > e…

This is tangential to your submission, but PDF is the file format I use for exercising any library that claims to be a declarative file format (ala https://github.com/kaitai-io/kaitai_struct_formats#readme )

Re: Show HN: I am building a new Python library to read/write PDF files

#8

Post by tmaly » Fri, Nov 18, 2022, 12:41 AM UTC

there is a Perl library that does this, but it only supports pdf 1.5

https://metacpan.org/pod/CAM::PDF

I have used it in the past.

Re: Show HN: I am building a new Python library to read/write PDF files

#9

Post by notacop31337 » Fri, Nov 18, 2022, 12:42 AM UTC

Spivak wrote: post #5

I wish you all the best! This space has a lot of stuff in it and they’re lacking in some aspect. And that’s not a admonishment, PDF is such a complicated format that there will never be a library that doesn’t come with asterisks — it’s just a matter of picking the thing you want your library to focus on and be good at and you can pretty easily be someone’s favorite lib.

My understanding is that this is largely because you're fighting an adversarial format provider in Adobe, I've read a few papers and journal entries on file format polyglotting, with some focus on PDF and approaches are constantly shifting in nature due to Adobe mooting pathways to success, I think it's partly for security and also IMO partly for obscurity as PDF is a horrific format in all reality except for human visual interpretation. Many organisations and industries ONLY produce public data via PDF and it makes the parsing of that information a far more difficult task (again, I suspect by design). After trying a few parsing options for PDF, I've come to hate it as a format. Luckily though, some options from a few cloud providers seem to be really hammering the problems complexity down, but the cost of the solutions can be very steep.

Re: Show HN: I am building a new Python library to read/write PDF files

#10

Post by Helmut10001 » Fri, Nov 18, 2022, 12:43 AM UTC

neilv wrote: post #4

Neat. Another use case for which you might want to think about a sample is extracting data from filled PDF forms. (That use case is why I once had to write a PDF parser.) Since you read&write, maybe also a use case of programmatically filling some form fields in an editable PDF form. Such pre-filling some of the fields for a particular Web site user in a dynamically-modified PDF form they download. But the source PDF…

I recently tried pdfplumber [1] to extract tables from (relatively) difficult formatted tables in PDF, and it was a great experience. I can recommend it. Before I ended up using pdfplumber, I tried at least three other PDF packages and they did not work as easily or as expected.

[1]: https://github.com/jsvine/pdfplumber