PI: Use __slots__

[MartinThoma]

More information

An awesome explanation on StackOverflow

How much is it worth?

It's about a 10x improvement in performance

Before:

After:

Text extraction speed according to the benchmark is not affected at all 🥲

[MartinThoma]

I'm running into https://stackoverflow.com/q/10857515/562769

[MartinThoma]

@pubpub-zz Is indirect_reference actually a property of PdfObjectProtocol / PdfObject? I've only seen it on Page and Destination

[pubpub-zz]

Quite. 99% of the time
This property is only initiated for objects attached to a pdfreader or a PdfWriter. The cloning process checks if this property exists to do some specific actions.

[MartinThoma]

There are two places where we assign indirect_reference:

PdfReader:

    def cache_indirect_object(
        self, generation: int, idnum: int, obj: Optional[PdfObject]
    ) -> Optional[PdfObject]:
        if (generation, idnum) in self.resolved_objects:
            msg = f"Overwriting cache for {generation} {idnum}"
            if self.strict:
                raise PdfReadError(msg)
            logger_warning(msg, __name__)
        self.resolved_objects[(generation, idnum)] = obj
        if obj is not None:
            obj.indirect_reference = IndirectObject(idnum, generation, self)
        return obj

PdfWriter:

    def _add_object(self, obj: PdfObject) -> IndirectObject:
        if hasattr(obj, "indirect_reference") and obj.indirect_reference.pdf == self:  # type: ignore
            return obj.indirect_reference  # type: ignore
        self._objects.append(obj)
        obj.indirect_reference = IndirectObject(len(self._objects), 0, self)
        return obj.indirect_reference

Those cause problems with the slots (potentially only for mypy)

[codecov]

Codecov Report

Base: 91.83% // Head: 91.83% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (ded82f6) compared to base (ea598dd).
Patch coverage: 90.90% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1524   +/-   ##
=======================================
  Coverage   91.83%   91.83%           
=======================================
  Files          33       33           
  Lines        6073     6077    +4     
  Branches     1193     1193           
=======================================
+ Hits         5577     5581    +4     
  Misses        321      321           
  Partials      175      175           

Impacted Files	Coverage Δ
pypdf/generic/_data_structures.py	89.97% <0.00%> (ø)
pypdf/_protocols.py	80.00% <100.00%> (ø)
pypdf/_reader.py	90.36% <100.00%> (ø)
pypdf/_writer.py	83.75% <100.00%> (ø)
pypdf/generic/_base.py	99.64% <100.00%> (+<0.01%)	⬆️

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[MartinThoma]

@pubpub-zz The interesting question is if FloatObject and BooleanObject ever get an attribute dynamically assigned. I only see dynamic attribute assignment for indirect_reference . I also only see it happening in

• PdfReader.cache_indirect_object
• PdfWriter._add_object
• DictionaryObject._clone

I guess all of them (or at least one) could assign indirect_reference to a float object, right?

[pubpub-zz]

Although unusual the indirect_reference can point to an FloatObject and NumberObject.

[MartinThoma]

Ok, then I'll close it. We need to find another way (or find a way to add indirect_reference to the object while having multiple inheritance)

[MartinThoma]

https://stackoverflow.com/questions/472000/usage-of-slots/472024#472024