Mark classes as not instantiable
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topic: feature
- Dominant language
- Python
- Stars
- 1.8k
- Forks
- 302
- Avg merge
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- Merged PRs (30d)
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Description
From python/typeshed#14558: Some classes (like re.Pattern) are not instantiable at runtime:
>>> import re
>>> re.Pattern()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot create 're.Pattern' instances
Currently, there is no working way to mark classes as such. Ideas to mark classes:
- Annotate the return type of
__new__asNoReturn/Never. - Set
__new__toNone(similar to how__hash__works). - A new decorator.
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the runtime example in the issue and the linked typeshed reference, python/typeshed#14558. Compare the proposed new annotations, setting new to None, and a decorator against existing typing behavior. Done means the project has agreed on a way to express that a class cannot be instantiated and has defined its expected semantics.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- tooling
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100