Python 3.14: StructuralCoverageTag.__init__() takes 1 positional argument but 2 were given

The coverage.py nightly Python test runs started failing on Python 3.14:

      def structural_coverage(label: int) -> StructuralCoverageTag:
          try:
              return STRUCTURAL_COVERAGE_CACHE[label]
          except KeyError:
  >           return STRUCTURAL_COVERAGE_CACHE.setdefault(label, StructuralCoverageTag(label))
  E           TypeError: StructuralCoverageTag.__init__() takes 1 positional argument but 2 were given

The other Python versions are fine.

Note: the deadsnakes nightly 3.14 that I've been using had been broken for a few weeks, so if this is a bug in 3.14, it could have been introduced since July 11th.

The breakage seems to be related to attrs 24.1.0 release.

Based on python-attrs/attrs#1326 (comment) I would guess that removing the dataclass_transform should fix it??

Thanks to both of you for the report and suggestions! I'm looking into this now and should have a fix out soon.

~~I'm somewhat surprised that this hasn't failed in our CI yet - we're running 3.14-dev, which pyenv is currently building from cpython main.~~ no, this is obvious, we're currently pinned to the prior version of attrs.

I also don't see how our noop decorator could have some runtime effect:

hypothesis/hypothesis-python/src/hypothesis/internal/conjecture/data.py

Lines 71 to 85 in 3c15b34

    
           if TYPE_CHECKING: 
        
               from typing import TypeAlias 
        
               from typing_extensions import dataclass_transform 
        
               from hypothesis.strategies import SearchStrategy 
        
               from hypothesis.strategies._internal.strategies import Ex 
        
           else: 
        
               TypeAlias = object 
        
               def dataclass_transform(): 
        
                   def wrapper(tp): 
        
                       return tp 
        
                   return wrapper

yeah, that's more like it:

(ok, with a repro in hand it's time to fix this!)

it's beautiful 🥲

cd8a71e seems to have fixed it, so my best guess is that it's (probably something in combination with) auto_attribs=True and you might be able to repro from that?

It's after midnight here though, so I'm just going to get the fix released and then go to bed 😅

Yes, I've finally managed to compile Python 3.14 on my Mac and apparently attrs can't find annotation-only fields on 3.14 anymore. You don't have to do anything, I've got a lead, I just want to understand better what's happening.

Ah, there's some other updates I wanted anyway in that PR, so might as well ship it 🙂

24.2.0 is out now, so you should be able to replace the whole thing with a single @attr.frozen or even @attrs.frozen since you depend on 22+ anyways.

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Python 3.14: StructuralCoverageTag.init() takes 1 positional argument but 2 were given #4067

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	if TYPE_CHECKING:
	from typing import TypeAlias

	from typing_extensions import dataclass_transform

	from hypothesis.strategies import SearchStrategy
	from hypothesis.strategies._internal.strategies import Ex
	else:
	TypeAlias = object

	def dataclass_transform():
	def wrapper(tp):
	return tp

	return wrapper

Python 3.14: StructuralCoverageTag.__init__() takes 1 positional argument but 2 were given #4067

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nedbat commented on Aug 5, 2024

hynek commented on Aug 5, 2024

Zac-HD commented on Aug 6, 2024

Zac-HD commented on Aug 6, 2024

hynek commented on Aug 6, 2024

Zac-HD commented on Aug 6, 2024

hynek commented on Aug 6, 2024

Zac-HD commented on Aug 6, 2024

hynek commented on Aug 6, 2024

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Python 3.14: StructuralCoverageTag.init() takes 1 positional argument but 2 were given #4067