On: Show HN: I am building a new Python library to rea...

[mdaniel]

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 <<
    /Producer (pdfTeX-1.40.10)
    /Creator (TeX)
    /CreationDate (D:20131209161146-08'00')
    /ModDate (D:20131209161146-08'00')
    /Trapped /False
    /PTEX.Fullbanner (This is pdfTeX, Version 3.1415926-1.40.10-2.2 (TeX Live 2009/Debian) kpathsea version 5.0.0)
    >> endobj

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

[fgeiger → mdaniel]

The PDF format is diverse enough for such a new project to still have plenty of incompatibilities. If you wanted to find many of them quickly, you might want to have a look at the documents used as test cases in other projects, such as pdf.js:

https://github.com/mozilla/pdf.js/tree/master/test/pdfs

[jonnycomputer → fgeiger]

Valuable practical, actionable advice

[mdaniel → mdaniel]

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 )

[BiteCode_dev → mdaniel]

J is for complex numbers. While math.sqrt(-1) raises an exception, cmath.sqrt(-1) returns 1j.

There is not distinction between values and references in python, everything is a reference. In fact, primitive like numbers are big struct objects in cpython, you cannot just manipulate the raw numbers.

The difference will rather wether you can modify an object or not. You cannot modify numbers, as they are immutable. Any increment will produce a new object. But you can modify a list. This gives the feeling numbers are passed as values and list are passed as references.

[lordgrenville → BiteCode_dev]

Parent was referring to "references" in the PDF spec (eg 42 0 R)